SB 

96 
AS 



Issued February 15, 1912. 

U. S. DEPARTMENT OF AGRICULTURE, 

BUREAU OF ANIMAL INDUSTRY.— Bulletin 143- 

A. D. MELVIN, Chief of Bureau. v ' {' 



THE MAINTENANCE RATIONS OF 
FARM ANIMALS. 



BY 



HENRY PRENTISS ARMSBY, Ph. D., LL. D., 

Director of the Institute of Animal Nutrition of The Pennsylvania 
State College; Expert in A nirnal Nutrition, 
Bureau of Animal Industry. 




WASHINGTON: 
GOVERNMENT PRINTING OFFICE. 
1912. 



Book 



7 



Issued February 15, 1912 

U. S. DEPARTMENT OF AGRICULTURE, 



BUREAU OF ANIMAL INDUSTRY.— Bulletin 143. 

A. D. MELVIN, Chief of Bureau. 



THE MAINTENANCE RATIONS OF 

FARM ANIMALS. 4 9* 

TtTI 



BY 



HENRY PRENTISS ARMSBY, Ph. D„ LL. D., 

Director of the Institute of Animal Nutrition of The Pennsylvania 
State College; Expert in Animal Nutrition, 
Bureau of Animal Industry. 




WASHINGTON: 
GOVERNMENT PRINTING OFFICE. 
1912. 




THE BUREAU OF ANIMAL INDUSTRY. 



Chief: A. D. Melvin. 

Assistant Chief: A. M. Farrington. 

Chief Cleric: Charles C. Carroll. 

Animal Husbandry Division: George M. Rommel, chief. 
Biochemic Division: M. Dorset, chief. 
Dairy Division: B. H. Rawl, chief. 

Inspection Division: Rice P. Steddom, chief; Morris Wooden, R. A. Ramsay, 
and Albert E. Behnke, associate chiefs. 

Pathological Division: John R. Mohler, chief. 
Quarantine Division: Richard W. Hickman, chief. 
Zoological Division: B. H. Ransom, chief. 
Experiment Station: E. C. Schroeder, superintendent. 
Editor: James M. Pickens. 
2 



fFP Op 1Q*»9 



LETTER OF TRANSMITTAL. 



U. S. Department of Agriculture, 

Bureau of Animal Industry, 
Washington, D. C, August 12, 1911. 
Sir : I have the honor to transmit herewith, and to recommend for 
publication in the bulletin series of this bureau, a manuscript entitled 
" The Maintenance Rations of Farm Animals," by Dr. Henry Pren- 
tiss Armsby, who has charge of the cooperative work in animal 
nutrition between this bureau and the Institute of Animal Nutri- 
tion of The Pennsylvania State College. The paper is based not 
only on Dr. Armsby's own work, but on that of other investigators 
as well, and is believed to cover the subject thoroughly. 
Respectfully, 

A. D. Melvin, 
Chief of Bureau. 

Hon. James Wilson, 

Secretary of Agriculture. 

3 



CONTENTS. 



Page. 



Introduction 7 

The fasting katabolism 8 

Purpose of the fasting katabolism 9 

The material katabolized 10 

Ash 10 

Fat 10 

Carbohydrates 10 

Protein 11 

Ratio of protein to total katabolism 11 

Influence of body fat 12 

Influence of surplus protein 13 

Relative constancy of energy katabolism 13 

The energy requirement for maintenance 16 

Replacement of nutrients 16 

Feed fat and body fat 16 

Carbohydrates and body fat 17 

Carbohydrates and feed fat 17 

Feed protein and body fat 17 

Fat or carbohydrates and protein 18 

Availability of energy. . „ 19 

Availability for cattle 20 

Availability for the horse — Zuntz and Hagemann's results 22 

Digestive work for crude fiber 23 

Work of mastication 23 

Computation of available energy 24 

Availability for the horse— Wolff's results 25 

Availability for carnivora 26 

Causes of increased metabolism 28 

Mechanical work 29 

Secretion 29 

Fermentation 29 

Digestive cleavages 30 

Intermediary metabolism 31 

Excretion 32 

The maintenance ration 33 

Relation of maintenance requirement to live weight 36 

Computation of relative body surface 38 

The maintenance rations of farm animals 39 

Cattle 39 

Sheep 48 

Swine 51 

The horse 55 

Zuntz and Hagemann's investigations 55 

Wolff's investigations 57 

Mtintz's experiments 62 

Grandeau and Le Clerc's results 62 

True maintenance and live- weight maintenance 6 



5 



6 CONTENTS. 

Page. 

Factors affecting the energy requirement 64 

Muscular activity 65 

Minor muscular motions 65 

Lying and standing 66 

Individuality 66 

Condition 67 

Age 68 

External temperature 69 

Regulation of body temperature 69 

Critical temperature 71 

Feed consumption a source of heat 71 

Isodynamic replacement 72 

Relation of maintenance ration to critical temperature 72 

Feed consumption lowers the critical temperature 73 

Critical temperature for farm animals 73 

The protein requirement for maintenance 74 

Protein katabolized during fasting 74 

Influence of previous feed 74 

Fasting katabolism variable 74 

The minimum of protein 75 

Influence of nonnitrogenous materials 76 

Relation to fasting katabolism 76 

Effect of surplus of protein 78 

Increases protein katabolism 78 

Utilization of protein limited 80 

Protein as a source of energy 81 

Storage of protein 82 

Fluctuations in body protein 83 

Relation to energy supply 84 

Value of nonprotein 88 

Minimum of protein for farm animals 89 

Cattle 89 

Sheep 94 

Swine 96 

The horse 97 

The optimum of protein 97 

Relative values of proteins 99 

Differences in constitution of proteins 99 

Absence of certain constituents 100 

Proportions of constituents 101 

Experimental methods 102 

Michaud's investigations 102 

Zisterer's experiments 104 

Results are qualitative 105 

Thomas's experiments 106 

Significance of results 108 



ILLUSTRATION. 



Page. 

Figure 1. — Availability of metabolizable energy of hay 35 



THE MAINTENANCE RATIONS OF FARM ANIMALS. 



INTRODUCTION. 

Feed is supplied to farm animals in order that they may either 
yield products useful to man as materials for human food and cloth- 
ing or serve him by the performance of mechanical work. But 
as a factory must first be supplied with enough power to keep in 
motion the shafting, belting, and other machinery before any product 
can be turned out, so the animal mechanism must be provided with 
sufficient feed to maintain the processes essential to life before any 
continued production is possible. The amount of feed required for 
this purpose is called the maintenance ration of the particular animal. 
It is the quantity of feed necessary simply to support the animal 
when doing no work and yielding no material product. If an animal 
receiving exactly a maintenance ration were subjected to a so-called 
balance experiment, there would be found an exact equality between 
income and outgo of ash, nitrogen, carbon, hydrogen, and energy, 
showing that the body was neither gaining nor losing protein, fat, 
carbohydrates, or ash. 

The word " maintenance " is sometimes used popularly in another 
sense to signify the total amount of feed required, for example, by a 
horse in order to perform his daily work or by a calf in order to make 
a normal growth. It is important to grasp the idea that, in its 
technical sense, the maintenance requirement means the minimum 
required simply to sustain life. The feed of the horse or calf would, 
from this point of view, be regarded as consisting of two portions; 
one of these is the maintenance ration, which if fed by itself would 
just support the horse at rest or the calf without growth, and the 
other the productive portion of the ration by means of which work 
is done or growth made. To recur to the illustration of the factory, 
the maintenance ration keeps the empty machinery running, while 
the additional feed furnishes the power necessary to turn out the 
product. 

It might seem at first thought that not much importance attaches 
to a study of the maintenance ration. The animal kept on such 
a ration yields no direct economic return and hence simple main- 
tenance feeding should be avoided, so far as practicable, and when 

7 



8 



MAINTENANCE RATIONS OF FARM ANIMALS. 



it appears desirable to practice it the observation of the skilled 
stockman, especially if supplemented by occasional weighings, will 
usually suffice to determine whether or not the end is being attained. 
Nevertheless, the subject has significance for practice as well as for 
science. A very considerable fraction of the feed actually con- 
sumed by farm animals — on the average probably fully one-half — 
is applied simply to maintenance. But if half of the farmer's feed 
bill is expended for maintenance, it is clearly important for him to 
know something of the laws of maintenance — how its requirements 
vary as between different animals, how they are affected by the con- 
ditions under which animals are kept, how different feeding stuffs 
compare in value, etc. — as well as to understand the principles gov- 
erning the production of meat, milk, or work from the other half of 
his feed. 

Physiologically, too, the maintenance requirement represents the 
demand of the basal life processes. The prime necessity of the organ- 
ism is to maintain itself. It must live before it can grow or propagate 
its kind, and in the phenomena of maintenance the fundamental 
processes of nutrition may be studied uncomplicated by the demands 
of growth, fattening, or reproduction. 

THE FASTING KATABOLISM. 1 

Unlike the operations of a factory, which cease when the power is 
shut off, the activities of the animal do not stop when food is with- 
drawn, but continue for a variable length of time at the expense of 
the materials of the body. It is as if the materials of the factory 
itself were being cut up and used for fuel under the boilers. Men have 
fasted voluntarily for 30 days or more without obvious permanent ill 
effects, and there are records of dogs having survived fasting periods 
of from 90 to 100 or more days. In the fasting animal at rest the vital 
activities are reduced, as it were, to their simplest terms, practically 
only those functions being active which are essential to continued life. 
The following approximate estimate by Zuntz of the factors of the 
katabolism of a fasting man may serve to give a general idea of their 
nature and relative importance. Tne figures show the oxygen con- 
sumption per minute of the various tissues and its percentage distri- 
bution : 

1 For references to the literature of the fasting katabolism compare : 
Magnus Levy. Von Noorden's Pathologie des Stoffwechsels, 2d od., I, 222-225 and 
310-315. 

Tigerstedt. Nagel's Handbuch der Physiologie des Menschen, I, 375-391. 
Lusk. The Science of Nutrition. 2d ed., 54—85. 

Benedict. Metabolism in Inanition. Carnegie Institution of Washington, Publication 
No. 77, II, 3G1-3G4. 

Armsby. Principles of Animal Nutrition, 3d ed., 80-92 and 340-347. 



THE FASTING KATABOLISM. 9 
Consumption of oxygen in fasting man weighmg 70 kilograms — Zuntz. 



Cubic 
centimeters 
per minute. 



Percentage. 



Circulation and respiration 



Voluntary muscles 



30.0 
112.0 



12. 45 
46.49 



Glands and other organs: 

Liver 

Small intestine 

Kidneys 

Pancreas 

Large intestine 

Salivary glands 



45.0 
25.1 
10.5 
9.3 
7.0 
2.0 



9S. 



9 



18.68 
10. 42 
4. 36 
3. 86 
2. 91 
.83 



41.06 



Total 



240.9 



100. 00 



According to the foregoing table nearly 60 per cent of the metab- 
olism of a fasting man is due to the work of the muscles, including 
that of respiration and circulation as well as the limited activity of 
the voluntary muscles, while somewhat over 40 per cent is due to the 
internal organs. No equally complete data are available for farm 
animals, but the supposition seems justified that their metabolism 
in its main features is not greatly unlike that of man. It may be 
noted that Zuntz and Hagemann found the energy expended in 
respiration and circulation by the horse in a state of rest to be, re- 
spectively, 4.7 and 5.01 per cent of the total metabolism. The sum 
of these — 9.71 per cent — is approximately comparable with the cor- 
responding figure for man. 



The animal body is primarily a transformer of energy. From the 
biochemical standpoint the essential phenomenon of physical life 
is the transformation of chemical into kinetic energy which accom- 
panies the breaking down of more or less complex molecules into 
simpler ones, and all vital activities are essentially manifestations of 
energy. In the fasting state this energy is derived from the store 
of chemical energy contained in the materials of the body itself. 
The very act of living, in the foregoing view of it, is synonymous 
with the expenditure by the organism of its stored-up capital of 
energy. The prime and dominating purpose of the fasting katab- 
olism, therefore, is to supply energy for the life actions. 

But since the necessary activities of the fasting organism are car- 
ried on by means of energy derived from the katabolism of materials 
contained in the tissues, the body's store of matter and of energy is' 
being constantly depleted. To prevent or replace this loss will re-' 
quire a corresponding supply of available material and energy in the 
feed. A knowledge of the kind and quantity of material katabolized 
during fasting and of the amount of energy liberated, therefore, is 
obviously the first step toward ascertaining the supply necessar3 T in 
the feed. 



PURPOSE OF THE FASTING KATABOLISM. 



10 



MAINTENANCE RATIONS OF FARM ANIMALS. 



THE MATERIAL KATABOLIZED. 



Ash. — The fasting organism suffers a continual loss of the so-called 
ash ingredients of its tissues, including both the sulphur and phos- 
phorus of its proteins and the more distinctly "mineral" elements, 
such as sodium, potassium, calcium, magnesium, chlorin, etc. These 
elements are just as essential to the existence of the animal as are 
the carbon, nitrogen, hydrogen, and oxygen of the so-called " or- 
ganic " compounds. 

The study of this branch of the subject, however, has hardly pro- 
gressed far enough as yet to permit a definite formulation of the ash 
requirements of domestic animals. The present paper, therefore, will 
be confined to a discussion of the maintenance requirements in the 
more limited and customary sense, including only those substances 
whose function it is wholly or in part to serve as sources of energy. 

Fat. — It is a familiar conception that fat formation is the body's 
method of disposing of surplus feed, and that the body fat is a 
store of reserve fuel material. The converse of this fact is equally 
familiar. The fasting or insufficiently fed animal loses fat and may 
reach a stage of extreme emaciation before the active tissues fail 
to perform their duties. Obviously, the fasting animal lives very 
largely upon its reserve fat. These conclusions from common obser- 
vation have been fully confirmed by comparative analyses of the 
carcasses of well-fed and of fasted animals as well as by the results 
of balance experiments in which the exact nature of the outgo from 
the body has been determined. 

Carbohydrates. — In addition to fat, the body stores up more or 
less nonnitrogenous matter in the form of glycogen in the liver and 
muscles. During the first few days of fasting this store of carbo- 
hydrates is also drawn upon, as is indicated by the fact that the 
respiratory quotient tends to approach unity, while later the amount 
katabolized becomes very small. This is well illustrated by Bene- 
dict's 1 experiments upon fasting men. The average results of a 
number of experiments in which men fasted for from two to seven 
consecutive days were as follows: 



Glycogen katabolized by fasting men — Benedict. 



Glycogen katabolized. 



Day. 



Number 
of sub- 
jects. 



Total. 



Per kilo- 
gram of 

body 
weight. 



Grams. 



Grams. 



First day.. . 
Second day. 
Third day.. 
Fourth day 
Fifth day... 
Sixth day . . 



14 
2 13 

6 



5 
2 1 



110.0 
40.3 
21.8 
23.3 
8.2 
21.7 
18.7 



1. 69 
.62 
.36 
.40 
.14 
.38 
.33 



Seventh day 



1 The Influence of Inanition on Metabolism. Carnegie Institution of Washington, D. C, 
1007, p. 464. 

2 Another subject showed a slight gain of glycogen. 



RATIO OF PROTEIN" TO TOTAL KATABOLISM. 11 

Protein. — Balance experiments, however, while confirming the 
conclusion that the loss of tissue in fasting usually consists chiefly 
of fat together with some carbohydrates, show that there is also a 
continual breaking down of body protein and a corresponding ex- 
cretion of urinary nitrogen. While the energy supply of the fasting 
animal is chiefly derived from the breaking down of nonnitrogenous 
material, the functional activity of the tissues necessarily involves the 
katabolism of a certain amount of protein. 

RATIO OF PROTEIN TO TOTAL KATABOLISM. 

Qualitatively, then, the katabolism of the fasting animal is substan- 
tially a katabolism of fat and of protein, and it becomes of interest 
to consider the quantitative relations between the two. Such a com- 
parison is best made on the basis of the amounts of energy liberated in 
the body in the katabolism of protein and of fat respectively. This 
aspect of the subject has been treated especially in an article by E. 
Voit 2 in which the results of a considerable number of fasting ex- 
periments are compiled and discussed. While some of Voit's com- 
putations are based on estimates, they are sufficiently accurate to 
outline definitely the main features of the fasting katabolism. In- 
cluding only experiments on animals well nourished at the beginning, 
he obtained the following averages for the percentage of the total 
energy liberated which was supplied by the katabolism of protein in 
the case of a number of different species. The results of the first day 
or two of fasting are not included in the averages. 



Proportion of energy derived^ from protein in fasting — E. Voit, 



Kind of animal. 


Live 
weight. 


Protein 
katabolism 
in per cent 

of total 
katabolism. 




Kilos. 
115.0 
63.7 
f 28.6 
\ 18.7 
I 7.2 
2.7 
.6 
3.3 
2.1 


Per cent. 

7.3 
15.6 
13.2 
10.7 
13.5 
16.5 
10.8 

7.4 
10.0 




Dog 


Rabbit 


Guinea pig 


Goose 


Hen 





While both the total and protein katabolism naturally showed a 
wide range as to absolute amount, whether per head or per unit of 
live weight, the ratio of protein to total katabolism proved notably 
uniform with only two exceptions. The experiments upon dogs, 27 
in number, included in the foregoing table furnished the basis for 
the following comparison, showing that in 74 per cent of the cases 
the ratio ranged from 10 to 17 per cent. 



1 Zeitscbrift fur Biolo^ie, vol. 41, p. 167. 



12 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Protein katabolism of dog m per cent of total katabolism. 



Number of cases. 



Absolute. 



Per cent. 



Less than 10 per cent . 

10 to 14 per cent 

14 to 17 per cent 

More tban 17 per cent 



4 
15 

5 
3 



14.8 
55.6 
18.5 
11.1 



27 



100.0 



It may be accepted as established, then, that in what may be spoken 
of as the normal fasting animal, in which the influence of the pre- 
vious feeding has disappeared and in which, on the other hand, the 
fat reserve has not been exhausted, the protein katabolism constitutes 
a fairly small percentage of the total katabolism, both being ex- 
pressed in terms of energy. 



It is clear, however, from the foregoing figures that the ratio of 
protein to total katabolism may vary considerably. The most impor- 
tant factor in this variation has been found to be the relative amount 
of fat contained in the body. So long as fuel material in the form 
of body fat is readily available, the amount of protein katabolized 
remains small. Usually, however, the store of fat in the body is less 
than that of protein, while in fasting its exhaustion is relatively 
more rapid. There comes a time, therefore, when the supply of non- 
nitrogenous material to the tissues begins to flag. When this hap- 
pens, the protein katabolism begins to increase — that is, when the 
supply of reserve fuel material runs low the organism begins to use 
the protein of its own tissues as a source of energy, and E. Voit 1 
shows that this occurs whenever the ratio of fat to protein remain- 
ing in the body falls below a certain limit. If the animal was origi- 
nally well fed, this rise in the protein katabolism occurs only shortly 
before death, from which fact it has received the name of the pre- 
mortal rise. In the case of very fat animals this point may never 
be reached, while, on the other hand, in a lean animal the protein 
katabolism may increase steadily from the very beginning of the 
fasting. The following three experiments upon a fat guinea pig, a 
moderately fat dog, and a lean rabbit, cited by Voit from Kubner's 
experiments, may serve to illustrate these three types of fasting 
katabolism : 



INFLUENCE OF BODY FAT. 



1 Loc. Cit, p. 502. 



CONSTANCY OF ENERGY KAT ABOLISH . 13 



Proportion of energy derived from protein — Buhner. 



Guinea pig. 


Dog. 


Rabbit. 


Day of 
fasting. 


Protein ka- 
tabolism in 
per cent of 
total ka- 
tabolism. 


Day of 
fasting. 


Protein ka- 
tabolism in 

total ka- 
tabolism. 


Day of 
fasting. 


Protein ka- 
tabolism in 
per cent of 
total ka- 
tabolism. 


2 


Per cent. 
10.4 
11.1 
11.0 
11.9 
11.8 
6.9 
11.2 
10.9 


2-4 


Per cent. 
16.3 
13.1 
15.5 
17.4 
20.0 


3 


Per cent. 
16.5 
23.6 
26.5 
29.8 
50.1 
96.4 


3 


10-11.... 
12 


5-7 


4 


9-12. 




13 


13-15.... 
16 


6 


14 


7 




17-18. . . . 


8 


9 





INFLUENCE OF SURPLUS PROTEIN. 



On the other hand, as Pettenkofer and Voit long ago showed, 1 
when an animal which has been previously receiving large amounts 
of protein is deprived of feed, the high protein katabolism which 
is observed during the first two or three days of fasting is accom- 
panied by a relatively smaller katabolism of fat. Thus in an experi- 
ment with a dog, cited on a subsequent page (p. 7±) to illustrate 
the initial fall of protein katabolism, respiration experiments were 
made on the second, fifth, and eighth days, with the following 
results : 

Katabolism of fasting dog — Toit. 



Day. 



Second dav 
Fifth day 
Eighth day 



Urinary 
nitrogen. ! 



Fat ka- 
tabo- 
lized. 



Grams. Grams. 

11. 6 86 

5. 7 103 

4.7 99 



Protein ka- 
tabolized in 
per cent of 
total ka- 
tabolism. 



26.2 
12.7 
11.1 



Obviously we have here the reverse of what takes place in the later 
days of fasting, viz, a gradual substitution of fat for protein as the 
readily available supply of the latter in the body is reduced. Doubt- 
less the effect would have been found to be still more marked on the 
first day of the fasting, when the protein katabolism was equivalent 
to 28.1 grams of nitrogen. 

RELATIVE CONSTANCY OF ENERGY KATABOLISM. 

The results which have just been considered regarding the nature 
of the material katabolized in fasting and the way in which fat, 



1 Zeitschrift fiir Biologie, vol. 7, p. 369. 



14 



MAINTENANCE RATIONS OF FARM ANIMALS. 



carbohydrates, and protein mutually replace each other as fuel ma- 
terial as one or the other is most available fully substantiate the 
assertion made on page 9 that the controlling factor in the katabo- 
lism of the fasting body is the demand for energy. As there stated, 
the body is essentially a converter of energy, and protein occupies a 
peculiar position in nutrition simply so far as it is a part of the 
necessary mechanism for this conversion. These facts can hardly 
have failed to suggest that the demand for energy must be relatively 
constant in the same individual, and that such is in fact the case has 
been demonstrated by a large number of experiments. 

For example, in the experiment by Voit upon a dog, just cited, the energy of 
the protein and fat katabolized on the three days, as computed from the data 
for the urinary nitrogen and for the fat katabolism, was as shown in the fol- 
lowing table, from which it appears that the total energy katabolized, especially 
when computed per kilogram of live weight, was approximately the same on 
the different days. 

Constancy of katabolism of fasting dog — Voit. 



Day. 


Live 
weight. 


Energy 

from 
protein. 


Energy 
from 
fat. 


Total 
energy. 


Total en- 
ergy per 
kilogram 

live 
weight. 






Kilos. 


Calorics. 1 


Calories. 1 


Calories. 1 


Calories. 1 


Second day 




32. 87 


289.3 


816.9 


1,106.2 


33.66 


Fifth day.. 




31.67 


142.2 


978.5 


1,120.7 


35. 38 


Eighth day 




30.54 


117.2 


942.4 


1,059.6 


34.70 



1 Throughout this bulletin the word " calorie " signifies the large, or kilogram, calorie, 
unless the contrary is specifically stated. 



The same constancy is illustrated by Rubner's experiments on a rabbit, a 
dog, and a guinea pig, whose relative protein katabolism was tabulated on 
page 13. The latter is repeated in the following table, together with the 
heat production as measured directly or the carbon dioxid excreted, which may 
be assumed to be an approximate measure of the energy katabolized. As the 
table shows, notwithstanding very considerable variations in the relative 
amount of protein katabolized, the total energy liberated in the body was rela- 
tively very constant. 



CONSTANCY OF ENERGY KATABOLISM. 15 



Constancy of katabolism of fasting animals — Rubner. 



. - 

Day oi lasting. 


Guinea pig. 


Dog. 


Rabbit. 


Protein ka- 
tabolism in 
per cent of 
total ka- 
tabolism. 


Heat pro- 
duction 
per kilo- 
gram. 


Protein ka- 
tabolism in 
per cent of 
total ka- 
tabolism. 


Carbon 
dioxid per 
kilogram. 


Protein ka- 
tabolism in 
per cent of 
total ka- 
tabolism. 


Carbon 
dioxid per 
kilogram. 


First 




C alories. 
149. 9 
162. 6 
156. 5 
140.5 
137.3 
150.6 
157.4 
155.6 
162.6 




GvdTflS. 
on 70 

ZU. /U 
Li . OO 




Grams. 


Second 


10. 4 

11. 1 
11.0 
11.9 
11.8 
6.9 
11.2 
10.9 








Third 


16. 3 


16.5 




Fourth 


17.99 




Fifth 




| 23.6 


j 17.26 


Sixth 












1 15.90 








Ninth 






) * 

j 29.8 

50.1 
} 96.4 


f 15. 90 
1 15. 65 


Tenth 


| 13.1 

15. 5 
17.4 
20.0 


/ 18. 70 
\ 17.86 
16. 13 
17. 06 
16. 12 








Twelfth 






1 17. 18 
15. 81 
\ 15. 95 
[ 15.90 


Thirteenth 












Fifteenth 






Sixteenth 










Seventeenth 


:::::::::::: 



































Benedict 1 lias obtained like results for the heat production of man as meas- 
ured directly by means of the respiration calorimeter. For example, in an 
experiment 2 covering seven days the following quantities of energy were ka- 
tabolized daily. 



Constancy of katabolism of fasting man — Benedict. 



Day of fasting. 


Energy 

from 
protein. 


Energy 
from fat. 


Energy 

from 
glycogen. 


Total 
energy. 


Energy 
per kilo- 
gram 
body 
weight. 


Protein 
katabo- 
lism in 
per cent 
of total 
katabo- 
lism. 




Calories. 


Calories. 


Calories. 


Calories. 


Calories. 


Per cent. 


First day 


318 


1, 175 


272 


1,765 


29.7 


17.7 


Second day 


286 


1,385 


97 


1,768 


29.9 


16.0 


Third day 


303 


1,471 


23 


1,797 


30.8 


17.0 


Fourth day 


248 


1,422 


105 


1.775 


30.8 


14. 3 


Fifth day 


221 


1,394 


34 


1.649 


29.0 


13.5 


Sixth day 


218 


1,244 


91 


1, 553 


27.5 


14. 1 


Seventh day 


204 


1,2S6 


78 


1,568 


2S.0 


13.2 



This constancy of the fasting katabolism evidently is in accord 
with the conception of it outlined on page 9 as the measure of the 
energy necessary to carry on the vital activities of the body. The 
functions of circulation, respiration, excretion, etc., must go on con- 
tinually in a state of so-called rest, the muscular tonus must be 
maintained and divers minor muscular movements executed. In 
the aggregate all these result in the expenditure of a relatively 
uniform amount of energy from day to day. This energy in the 

1 The Influence of Inanition on Metabolism. Carnegie Institution of Washington, 1907, 
Publication No. 77. 

2 Experiment No. 75 on S. A. B., pp. 188, 483, and 496. 



16 MAINTENANCE EATIONS OF FARM ANIMALS. 

fasting animal is supplied mainly by the katabolism of protein and 
fat. In the intermediate stages of fasting, as has been shown, the 
katabolism is largely that of fat, but the ratio between fat and 
protein katabolizecl may differ widely according to circumstances. 
In other words the protein requirement, or at least the amount of 
protein used, may vary, while the energy requirement remains nearly 
constant. The fasting organism requires a definite quantity of 
energy, but seems more or less indifferent as to its source. 

THE ENERGY REQUIREMENT EOR MAINTENANCE. 

In the fasting animal the store of potential energy in the body 
is diminished daily by the amount required to carry on the vital ac- 
tivities, this amount being, as just shown, relatively constant. In 
order to prevent such a loss and maintain the store of body energy, 
it is evident that a corresponding quantity of energy must be sup- 
plied in the feed and that a maintenance ration is one which supplies 
this requisite quantity. 

REPLACEMENT OF NUTRIENTS. 

For this purpose experiments have shown that the various di- 
gestible nutrients may replace each other or the ingredients of the 
body through a very wide range. 

FEED FAT AND BODY FAT. 

Fat fed to a previously fasting animal diminishes or suspends the 
loss of body fat. The following averages of Pettenkofer and Voit's 
experiments, 1 computed from Atwater and Langworthy's digest, 2 
may serve to illustrate this substitution of feed fat for body fat : 



Replacement of body fat by feed fat — Pettenkofer and Voit. 



Food. 


Number 
of experi- 
ments. 


Gain or loss by 
body. 


Nitrogen. 


Fat. 


None 


5 
2 
1 


Grams. 
-6. 64 
-4.90 
-7. 70 


Grams. 

- 97.76 

- 16.25 
+ 113.60 


100 grams fat 







The smaller amount of fat not only diminished the protein katabolism but 
also largely reduced the loss of fat from the body. While the larger amount 
of fat showed a tendency to increase the protein katabolism, it not only sus- 
pended the loss of body fat but caused a storage of fat in the organism. Of 
course there is no means of distinguishing in such a case between feed fat and 



1 Zeitschrift fur Biologie, vol. 5, p. 370. 

2 U. S. Department of Agriculture, Office of Experiment Stations, Bulletin 45. 



REPLACEMENT OF NUTRIENTS. 



17 



body fat, but it is most natural to suppose that the resorbed fat of the feed, 
being already in circulation in the body, is more easily accessible to the active 
cells than the stored-up fat of the adipose tissue and is therefore metabolized 
in preference to the latter. 



CABBOHYDBATES AND BODY FAT. 



Experiments precisely similar to those on fat just described show 
that carbohydrates may also diminish or suspend the loss of body fat. 
This may be illustrated by the results of three experiments upon a dog 
by Rubner. 

Replacement of body fat by carbohydrates — Rubner. 



Food. 



None 

76.12 grams cane sugar. 
104.97 grams cane sugar 

None 

42.96 grams starch 

None 

57.38 grams starch 



Total nitro- 
gen of ex- 
creta. 



Grams. 
1.94 
1. 45 
1.07 
1.42 
1.53 
2.00 
1.52 



Total car- 
bon of ex- 
creta. 



Grams. 
38. 18 
43. 19 
47. 78 
26. 47 
33. 28 
31.53 
39. 67 



CABBOHYDBATES AND FEED FAT. 



Rubner substituted dextrose for fat in the diet of a dog receiving 
also a fixed amount of lean meat. The results of this substitution 
are given in the following table, and show that with the larger 
amount of dextrose in place of the fat previously fed the loss of body 
fat was prevented : 

Replacement of feed fat by carbohydrates — Rubner. 



Ration. 


Feed per day. 


Gain or loss by- 
animal. 


Meat. 


Fat. 


Dextrose. 


Nitrogen. 


Carbon. 


Meat and fat 


Grams. 
300 
300 
300 
300 
300 


Grams. 
42 
50 


Grams. 


Grams. 
+1.81 
+ .10 
+1.78 
+2.28 
+1.98 


Grams. 
+1.27 
+9.31 
-7.44 
-8. 15 
+6. 21 


Do 




Meat and dextrose 


63.7 
79.7 
115.5 


Do 




Do 









FEED PBOTE1N AND BODY FAT. 

It has already been shown that body protein may replace body fat 
in the katabolism of the fasting animal. A similar substitution of 
feed protein for body fat may take place. When protein is given 
to a previously fasting animal it is a well-known fact that the 
nitrogen of the protein is rapidly split off and excreted, while the 
nonnitrogenous portion of the molecule serves as a source of energy 
8489°— Bull. 143—12 2 



18 



MAINTENANCE RATIONS OF FARM ANIMALS. 



to the organism. (Compare pp. 78 to 82.) This nonnitrogenous 
residue can be substituted for body fat, as is illustrated in an experi- 
ment by Kubner in which extracted lean meat was given to a fasting 
animal, with the result tabulated below: 



Replacement of body fat by protein — Rubner. 





Nitrogen 
of food. 


Nitrogen 
katabo- 
lized. 


Fat katab- 
olized. 


Fasting 


Grams. 



Grams. 
5. 25 
26. 37 


Grams. 
84. 39 
28. 37 


Fed 


35.22 




Difference 




+21.12 


-56. 02 







FAT OR CARBOHYDRATES AND PROTEIN. 



A certain minimum of protein is essential to the maintenance of 
the protein tissues of the body, but feed protein in excess of this 
amount undergoes rapid katabolism and serves substantially as a 
source of energy. Such an excess of protein in the feed can be re- 
placed by nonnitrogenous nutrients, particularly the carbohydrates. 
This effect of fat or carbohydrates as a substitute for protein may be 
illustrated by the following tabulation of the average results of a 
number of Pettenkofer and Voit's experiments : 

Replacement of feed protein by fat or carbohydrates — Pettenkofer and Voit. 



Rations. 



Protein only: 

Series I 

Average of all (22 experiments) 
Protein and fat: 

1(10 grams fat (1 experiment) . . , 

200 grams fat (5 experiments).. 
Protein and carbohydrates: 

Starch (8 experiments) 

Grape sugar (3 experiments) . . . 



Feed per day. 



Gain or loss by body 



Meat. 



Grams. 
1,500 
1,500 

500 
500 

500 
500 



Fat. 



Grams. 



100 
200 



5.3 



Starch. 



Grams. 



200 



Grape 
sugar. 



Grams. 



Nitrogen. 


Carbon. 


Grams. 


Grams. 





+ 3.3 


+0.6 


+ 8.7 


+ .3 


+27.1 


- .6 


+67.3 


-1.8 


+ 9.0 


-1.3 


+ 7.2 



It appears, then, that all the principal nutrients may serve to supply 
energy to the body, and the facts just considered show a remarkable 
degree of flexibility on the part of the animal organism as regards 
the nature of the material which can be utilized for its metabolism. 
Aside from the small minimum of protein required, the metabolic 
activities of the body may be supported now at the expense of the 
stored body fat, now by the body protein, and again by the protein, 
the fats, or the carbohydrates of the feed. Whatever may be true 
economically, physiologically the welfare of the mature animal is not 
conditioned upon any fixed relation between the classes of nutrients 
in its feed supply apart from the minimum requirement for protein. 



MAINTENANCE RATIONS OF FARM ANIMALS. 



19 



AVAILABILITY OF ENERGY. 

Since the chief function of the feed, aside from a minimum of 
protein, is to supply energy, it would be natural to suppose that the 
quantity of energy liberated in the body by the oxidation of any 
given substance (i.e., its metabolizable energy) would be the measure 
of its nutritive value. If one gram of starch, for example, can liberate 
4.2 calories of energy in the body and a gram of fat 9.5 calories, 
apparently the relative values of the two should be in proportion to 
these figures. But while the metabolizable energy of the feed rep- 
resents the maximum amount of energy which can be extracted from 
it by the organism, it does not follow that all of it can be utilized for 
maintenance. Energy is not something which can be fed into the 
organism regardless of its source, like fuel under a boiler. Whatever 
energy is in essence, so far as the animal is concerned it is carried 
as chemical energy by the compounds of the feed, and these must be 
such as can take part in the actual chemical changes occurring in the 
cells if their energy is to be utilized. The body can not, like a heat 
engine, avail itself of energy in the kinetic form. It is quite con- 
ceivable that a compound might be resorbed from the digestive tract 
and then simply oxidized to get rid of it without its entering into 
the cell metabolism. Its energy- would be metabolized, that is, con- 
verted into the kinetic form, but it would be simply a source of heat 
and not of other forms of energy. Somewhat similar is the case of 
the chemical changes occurring in the digestive tract. Some of these, 
notably the fermentations of the feed, set free energy as heat, yet 
this energy plays no part in the actual metabolism of the tissues. It is 
clear, then, that we are not warranted in concluding that because, 
for example, a fasting animal breaks down body substance equivalent 
to 10 therms per day, therefore a ration containing 10 therms of 
metabolizable energy will suffice to maintain the animal. That will 
depend upon how completely the body is able to use the 10 therms of 
metabolizable energy supplied to it. In other words, the energy must 
not only be present, but it must be available energy. 

If the metabolizable energy were all available to protect body 
tissue from oxidation, then giving feed to a fasting or partially 
fasting animal would be practically the substitution of one kind of 
fuel for another, and the total heat production would remain the 
same. It is, however, an observation as old as the time of Lavoisier 
that the consumption of feed tends to increase the heat production 
of an animal. That investigator observed the oxygen consumption 
of man to increase materially (about 37 per cent) after a meal, and 
subsequent experiments by a large number of investigators have fully 
confirmed these earlier results, so that the fact of an increased metab- 
olism consequent upon the ingestion of feed is undisputed. It is 
especially to the investigations of Zuntz and his associates that we 



20 



MAINTENANCE RATIONS OF FARM ANIMALS. 



owe the unquestionable demonstration of this fact and of its signifi- 
cance in relation to the nutritive values of feeding stuffs. 

These relations may perhaps be more clearly apprehended through 
an illustration taken from actual experimental work. 

AVAILABILITY FOB CATTLE. 

In an experiment by Armsby and Fries 1 a steer averaging 373.7 
kilograms live weight was fed daily 3.2 kilograms of timothy hay, 
an amount known to be insufficient for maintenance. The potential 
energy contained in the feed, the losses in the various excreta, and 
the metabolizable energy of the ration were determined, with the 
following results: 

Per day and head. 



3.199 kilos timothy liay 12. 618 

Excreta : Therms. 

4.786 kilos feces 5.247 

3.943 kilos urine .627 

0.079 kilo methane 1.057 

Total 6. 931 

Metabolizable energy of ration 5. 687 



A balance experiment with the respiration calorimeter showed, 
as was expected, that the steer was living in part at the expense of 
his own tissues, the total loss of protein and fat being equivalent 
to 2.377 therms 2 per day. 

In the period immediately following this one the same steer ate 
per day 5.194 kilograms of the same timothy hay, all the other condi- 
tions of the experiment being as nearly identical as possible. The 
metabolizable energy of this larger ration, determined in the manner 
just indicated, was 9.262 therms, 3 while a balance experiment showed 
that the loss of protein and fat had been reduced to the equivalent 
of 0.357 therm. 3 

The following comparison of the two periods can therefore be 
made: 



Available energy of timothy hay. 




Ration. 


Metaboliz- 
able 
energy of 
ration. 


Energy of 
fat and 
protein lost 
by animal. 




Kilos. 
5.294 
3.199 


Therms. 
9.2G2 
5.687 


Therms. 
0.357 
2. 377 


Do 




2.095 


3. 575 


2.020 




I _ 



1 Bureau of Animal Industry, Bulletin 128, pp. 177 and 184. 

a Computed to 12 hours' standing. 

a Corrected to the same live weight as in Period III. 



AVAILABILITY OF ENERGY FOR CATTLE. 



21 



On the lighter ration, the steer supplemented the energy derived 
from its feed by 2.377 therms derived from the katabolism of its own 
fat and protein, but when 2.1 kilograms of timothy hay was added to 
the ration, the amount of energy which had to be furnished by the 
body tissues was reduced to 0.357 therm. In other words, 2.1 kilo- 
grams of timothy hay supplied 2.020 therms of energy which was 
available to support the necessary bodily activities and which, there- 
fore, could replace an equal amount which would otherwise have been 
derived from the katabolism of body substance. This was the con- 
tribution which this amount of hay made to the maintenance of the 
steer. 

But the 2.1 kilograms of timothy hay added to the ration supplied, 
as the table shows, 3.575 therms of metabolizable energy. Clearly, 
then, a unit of metabolizable energy supplied by the digestible matter 
of the hay was less efficient than the same amount supplied by body 
substance. Only 56.5 per cent of it could be substituted for that pre- 
viously supplied by the katabolism of the fat and protein of the body 
of the steer, while the remaining 1.555 therms, or 43.5 per cent, sim- 
ply increased the heat production of the animal, the latter being as 
follows : 



It is customary in such a case to speak of the 2.020 therms as the 
available energy of the hay added to the basal ration of Period III 
and to say that 56.5 per cent of the metabolizable energy of the hay 
was available. Such a method of statement does not necessarily 
imply that the remaining 43.5 per cent served no useful function in 
the body, but simply asserts that the net result to the organism was 
the same as if 56.5 per cent of the metabolizable energy were sub- 
stituted unit for unit for energy derived from the katabolism of body 
substance and as if the remaining 43.5 per cent were useless. What 
the experiment really shows is that a unit of metabolizable energy 
in the hay had only 56.5 per cent of the value for maintenance of a 
unit of metabolizable energy in the body substance (chiefly fat) 
previously katabolized, but the first method of expression is both 
common and convenient and may be retained. 

Experiments by the same authors on several other feeding stuffs have 
given results of the same general character as those just quoted. Of the 
metabolizable energy of these feeding stuffs, as directly determined in each ex- 



Daily heat production. 1 



Therms. 



On the heavier ration 
On the lighter ration. 



9. 619 
8. 064 



1 Corrected to 12 hours standing. 



22 



MAINTENANCE RATIONS OF FARM ANIMALS. 



periinent, the following percentages were found to be available in the above 
sense, while the remainder simply served to increase the heat production : 

Average availability of metabolizable energy. 



Per cent. 

Timothy hay, 5 experiments 56.32 

Clover hay, 2 experiments 58. 47 

Corn meal, 1 experiment 69. 12 

Wheat bran, 2 experiments 55. 36 

Mixed grain (1 part wheat bran, 3 parts corn meal, 3 parts 

linseed meal O. P. ) , 4 experiments 57. 42 



Kellner's 1 extensive investigations upon the metabolism of fattening cattle 
have likewise demonstrated that in the productive feeding of these animals 
only part of the metabolizable energy supplied in excess of the maintenance 
ration is recovered in the gain produced, the remainder being converted into 
heat, so that the heat production increases with the amount of feed consumed. 

AVAILABILITY FOR THE HORSE ZUNTZ AND HAGEMANN'S RESULTS. 

The foregoing results upon cattle have been cited because they 
illustrate simply and clearly the basic conception of the availability 
of feed energy and also because they are, so far as the writer is 
aware, the first experiments upon farm animals on submaintenance 
rations in which the complete balance of matter and of energy for 24 
hours has been determined. Zuntz and Hagemann 2 , however, had 
shown several years before in an extensive investigation that the in- 
creased metabolism which Zuntz and his associates had observed in 
dogs and men as resulting from the ingestion of food was even more 
marked in the case of the horse. 

In their investigations the respiratory exchange of the animal was determined 
by the Zuntz method in short periods at various intervals after the consump- 
tion of more or less diverse rations, a small correction being added for cuta- 
neous and intestinal respiration. By combining these results with those of a 
number of separate digestion trials in which the nitrogen and carbon of the 
feed and of the visible excreta were determined, an approximate determination 
of the total energy metabolism of the animal was also possible. 3 

For example, on the average of a number of experiments in which the metab- 
olism shortly before feeding in the morning, shortly after feeding, and some 
hours later was determined by the methods just outlined, the following results, 
computed per kilogram per minute were obtained.* 




Energy- 
liberated. 



Fasting 

36 minutes after feeding 
hours after feeding. . . 



Gram- 
calories. 
16. 929 
18.510 
18. 787 



1 Die Landwirtschaftlichen Versuchs-Stationen, Band 53, and Ermihrung der Land- 
wirtshaftlichen Nutztiere. 

2 Landwirtschaftliche Jahrbiicher, vol. 27, Ergiinzungsband III. 

3 For a more complete account of the method, compare Armsby, Principles of Animal 
Nutrition, pp. 386-387. 

* Loc. cit., p. 282. 



AVAILABILITY OF ENERGY FOE THE HORSE. 



23 



It was also found that coarse fodder (hay) produced a much more marked 
effect than did grain. The following comparison of the average of the experi- 
ments of period c on an exclusive hay diet with that of the experiments of 
period / on a mixed ration illustrates this fact. 1 





Period c. 


Period /. 


Ration: 

Hay 


hours.. 

kilos.. 

do.... 


2.6 

About 10. 5 


2.8 

4. 75 
6.00 


Straw 


do.... 




1.00 


Total digested nutrients (fat X 2.4) 

Per kilogram and minute: 

Oxygen consumed 

Carbon dioxid given off 

Energy set free (computed) 

Energy katabolism per day and head 


grams.. 

cubic centimeters. . 

do.... 

gram-calories. . 

calories.. 


4, 125 

3.9837 
3. 6586 
19. 552 
12,450 


5,697 

3. 6986 
3. 6695 
18. 339 
11,678 



DIGESTIVE WORK FOR CRUDE FIBER. 

Zuntz and Hagemann estimate the fuel value of the total digestible nutrients 
in the feed of the horse (including digestible crude fiber and digestible fat X 
2.4) at 3.96 calories per gram, and on the basis of experiments on man made by 
Magnus-Levy in Zuntz's laboratory they assume that 9 per cent of the metabo- 
lizable energy of the digestible nutrients as thus computed is expended in 
their digestion. The hay ration of the foregoing table contained 1,572 grams 
less of (estimated) digestible nutrients than the mixed ration. The corre- 
sponding expenditure of energy in the digestion of these nutrients (9 per cent 
of their metabolizable energy) equals 580 calories. Accordingly the energy 
katabolism should have been 580 calories less in period c than in period /. 
It was actually 772 calories greater, a difference of 1,352 calories. This differ- 
ence is ascribed to the presence in the hay ration of 648 grams more of total 
crude fiber and corresponds to 2.086 calories per gram of the latter. 

WORK OF MASTICATION. 

The foregoing computations relate to the expenditure of energy in the diges- 
tion of the food after it has entered the stomach. The same authors have also 
determined the increase in the gaseous exchange caused by mastication, deglu- 
tition, etc. For this purpose they compare 2 the excretion of carbon dioxid and 
the consumption of oxygen during the time actually occupied in eating with 
the corresponding amounts during rest, as shown by the average of a number of 
experiments made under identical conditions. On the assumption that the pro- 
tein metabolism is unaltered, the amounts of carbohydrates and fat metabo- 
lized and the corresponding amounts of energy are calculated. The following 
is a summary of the results computed per kilogram of feed : 



Energy expended in mastication of 1 kilogram — Zuntz and Hagemann. 



Feed. 


Number 

of 
experi- 
ments. 


Oxygen 
consumed. 


C0 2 
excreted. 


Equivalent 
energy. 


Hay 


8 
8 
8 
2 
7 


Liters. 
12. 964 
33.840 
20. 072 
7. 133 
6. 171 


Liters. 
10.679 
27.813 
17.677 
6.205 
4.980 


Calories. 
64. 17 
167. 44 
100. 79 
35.72 
30.42 
47.00 
13.80 


Hay, oats, and cut straw 

Maize and cut straw (6:1) 

Green alfalfa 





















1 Loc. cit, pp. 276-279. 2 Loc. cit., p. 271. 



24 



MAINTENANCE RATIONS OF FARM ANIMALS. 



As was to have been expected, the work of mastication proves to be much 
greater in the case of hay than in that of grain. Maize gave a remarkably low 
result, while the lowest was obtained with green fodder. Even when the results 
on the latter are computed per kilogram of dry matter, they are still about 40 
per cent lower than those on hay. A few experiments on old horses with defec- 
tive teeth gave somewhat higher results for the mixture of oats and cut straw. 

While pointing out that, as the above results show, other factors than the 
amount of crude fiber influence the work of mastication, they nevertheless 
believe that a sufficiently close approximation for practical purposes may be 
reached by computing the work of mastication upon the amount of crude fiber 
present, which gives an average of 0.565 calorie per gram, and using this factor 
to compute the work of mastication of the average ration. Adding this factor 
to the 2.086 calories computed for the work of digestion of one gram of fiber 
gives a total of 2.65 calories per gram of total crude fiber as representing the 
work of mastication together with the extra expenditure of energy in digestion. 



In brief, then, Zuntz and Hagemann compute the available energy, 
or maintenance value, of a feeding stuff for the horse as follows: 
First, the metabolizable energy is computed at the rate of 3.96 calo- 
ries per gram of total digestible matter, including the digestible crude 
fiber and the digestible fat multiplied by 2.4. Second, from the 
metabolizable energy thus computed there is subtracted 9 per cent 
for the work of digestion and in addition 2.65 calories for each gram 
of total crude fiber present. 

The method of computation may be conveniently illustrated from 
the data given by Langworthy 1 for timothy hay. Zuntz and Hage- 
mann 's factors, recalculated per pound for convenience, become, for 
metabolizable energy, 1.796 therms ; for crude fiber, 1.202 therms. On 
this basis the calculation of the available energy of the hay would be 
as follows: 



COMPUTATION OF AVAILABLE ENERGY. 



Available energy in 100 pounds of timothy hay. 



Digestible nutrients : 

Protein 

Crude fiber 

Nitrogen-free extract 
Fat (1.18X2.4) 



Pounds. 



1. 25 
12. 39 
21. 29 

2. 83 



Total crude fiber. 



37. 72 
29. 00 



Therms. 



Metabolizable energy (1.796 therms X 37.72) 

Work of digestion : 

9 per cent of metabolizable (67.75 therms X 0.09) 
Additional for crude (1.202 therms X 29) 



67. 75 



/ 



Therms. 
_ 6.10 

_ 34.86 



Total 



40. 96 



Available energy (maintenance value) 



26. 79 



1 U. S. Department of Agriculture, Office of Experiment Stations, Bulletin 125, p. 14. 



AVAILABILITY OF ENERGY FOR THE HORSE. 



25 



As is evident from the brief description given of the methods by 
which the factors are reached, this method of computation is not 
claimed by its authors to be scientifically exact, but they believe it to 
be a sufficiently close approximation on which to base computations 
of rations in practice. 

Zuntz and Hagemann's conclusions have been subjected to con- 
siderable criticism, the two principal points being, first, their esti- 
mate of 9 per cent for the work of digestion, based upon the results 
of experiments on man ; and, second, and more especially, the assump- 
tion that the metabolism for 24 hours may be computed from the 
results of comparatively short respiration experiments. Qualita- 
tively, Zuntz and Hagemann have clearly demonstrated the very 
considerable expenditure of energy by the horse in the digestion of 
his feed, as well as the fact that this expenditure is much greater 
with coarse fodders than with grain, and they were the first to point 
out that this expenditure of energy must be taken account of in esti- 
mating the values of feeding stuffs. There may be a difference of 
opinion as to the quantitative worth of their figures, and certainly 
investigations by more direct methods, involving fewer assumptions 
and complex calculations, are greatly to be desired, but until such 
results are obtained we may continue to use provisionally those 
reached in the manner just described. 

AVAILABILITY FOB THE HOBSE WOLFF'S BESULTS. 

His extensive investigations upon the working horse, made at 
Hohenheim in 1877 to 1894 1 and antedating the investigations thus 
far mentioned, led Wolff to a still simpler approximate method of 
estimating what in a sense corresponds to the available energy ol 
the feed of the horse. 

In Wolff's experiments, the horse performed a measured amount of work 
which was so adjusted in different periods as to be as nearly as possible in 
equilibrium with the feed consumed. This was considered to be the case when 
the live weight of the animal remained substantially unchanged for a con- 
siderable period and when the urinary nitrogen did not show an increase as a 
consequence of the additional work done. By comparing the work performed 
on a basal ration with that which could be done with a heavier one, the ratio 
of the work done to the additional feed consumed was established within the 
limits of error of the method, this being the prime object of the experiments. 
This being determined, however, it was a simple matter to compute the amount 
of feed corresponding to the total work done, while subtracting this from the 
total ration would give the maintenance ration. The results of these compari- 
sons, made on the basis of the so-called " digestible nutrients " of the rations 
(the digestible fat being multiplied by 24) are considered on subsequent pages. 

On the average of a considerable number of comparisons, it was 
found that the digestible nutrients from coarse fodders were less 



1 Compare pp. 57 to 62. 



26 



MAINTENANCE RATIONS OF FARM ANIMALS. 



efficient both for work production and for maintenance than were 
those derived from grain, and Wolff also cites the results of Gran- 
deau and Le Clerc's experiments in Paris which show the same 
general result. Wolff shows, however, that if the digestible crude 
fiber be omitted from the comparisons, the ratio between fiber-free 
nutrients and the work performed is comparatively uniform and 
also that this assumption yields uniform results for the fiber- free 
nutrients required for maintenance. He therefore concludes that the 
crude fiber in the rations of the horse is apparently valueless and that 
the remaining digestible nutrients may be regarded as of equal value 
whether derived from grain or from coarse fodders. Expressed in 
the light of our present conceptions, this is practically equivalent to 
saying that the expenditure of energy in digestion is proportional to 
the metabolizable energy of the crude fiber, or that the available 
energy is proportional to the amount of fiber-free nutrients. 

Wolff is careful to say that the digestible crude fiber is apparently 
valueless, and virtually regards the amount of crude fiber as furnish- 
ing a convenient empirical measure of the difference in the nutritive 
value of the digestible nutrients of coarse fodder as compared with 
those of grain. That such is the case is doubtless explained in part 
by the rather limited variety of feeding stuffs employed in the experi- 
ments. The coarse fodder was meadow hay, with, in some cases, a 
small addition of straw, while the grain was usually oats, partially 
replaced in some cases by other feeds. Whether the same relation 
between fiber-free nutrients and work done would hold in widely 
different rations is not apparent. 

It should be borne in mind that in reality Wolff's results are rela- 
tive only. They do not show the actual amount of available energy 
in the feed or ration, but only that it is proportional to the fiber-free 
nutrients. The energy of the latter would differ considerably from 
the available energy as computed by Zuntz and Hagemann's method, 
first, because it does not include the deduction of 9 per cent for di- 
gestive work ; and, second, because it assumes a uniform value of zero 
for crude fiber, while Zuntz and Hagemann's method gives the crude 
fiber a negative value if it has a digestibility of less than 55 per cent. 
The values computed according to Wolff's method from the fiber-free 
nutrients are therefore considerably higher than Zuntz and Hage- 
mann's figures. 

AVAILABILITY FOR CARNIVORA. 

For many years it was taught, in accordance with Rubner's theory 
of " isodynamic replacement" (compare p. 72), that with carnivora 
the nutrients were of value in proportion to their content of metab- 
olizable energy. Rubner's own later investigations, 1 however, have 



1 Die Gesetze des Energieverbrauchs bei der Ernahrung. 



AVAILABILITY OF ENEBGY FOR CARNIVOBA. 



27 



shown that what is true of the feeding stuffs consumed by horses and 
cattle is also true of nearly pure nutrients fed to dogs. With these 
subjects it is possible to use the fasting state as the basis of compari- 
son, which considerably simplifies the investigations. The experi- 
ments were made at a comparatively high temperature, namehy, about 
33° C., a fact which is of importance, as will appear later, in the inter- 
pretation of the results. 

An experiment in which nearly enough fat was fed to supply the 
requirements of the organism for energy gave the following results 
per kilogram live weight, stated in a form which is somewhat differ- 
ent from that used by Rubner but which in substance is identical 
with it : 

Availability of energy of fat — Rubner. 





Metaboliz- 

able 
energy of 
feed per 
kilogram 

live weight. 


Loss by 
body per 
kilogram 
live 

weight. 




Calorics. 
53.4 



Calories. 
7.5 
54.0 






53.4 
87.08 


46.5 









This result appears somewhat remarkable in view of the fact that 
the comparison is virtually with body fat. Literally interpreted, it 
means that the energy of feed fat is only 87 per cent as valuable as 
the energy of body fat plus a little protein. If this be true, it implies 
a larger expenditure of energy in the digestion of fat than now seems 
probable, since the katabolism of resorbed feed fat can hardly differ 
greatty from that of body fat. Rubners figure is the result of a 
single experiment and unfortunately it enters into the computation of 
all the other results. A redetermination of this factor is much to be 
desired. 

In two other experiments, lean meat nearly equivalent to the main- 
tenance requirement was fed. The meat contained a small amount of 
fat, the average metabolizable energy of the feed per kilogram live 
weight being distributed as follows : 

Calories. 

In protein 56. 7 

In fat 4.95 



61. 65 



28 MAINTENANCE RATIONS OF FARM ANIMALS. 

Using the data afforded by the experiment on fat, the availability 
of the energy of the protein may be computed as follows : 



Availability of energy of protein — Rubner. 





Metabolizable 
energy of feed 
per kilogram 
live weight. 


Loss by 
body per 
kilogram 
live weight. 


Meat fed 


Calories. 

61.65 


61.65 
4.95 
56.70 
Per cent. 

67.53 


Calories. 
8.90 
51.50 

42. 60 
4.31 
38.29 


Fasting 


Difference 


Difference due to fat 


Difference due to protein 


Percentage available 







The difference between the percentage available and 100 shows, of 
course, the proportion of the metabolizable energy of the feed which 
was expended in increasing the total metabolism as measured by the 
heat production. This increase of the metabolism of the body is 
called by Rubner the " specific dynamic effect " of the several nutri- 
ents. Rubner's final average results are contained in the following 
table. It should be clearly understood that they are not applicable 
to the " digestible nutrients " of the feed of herbivora. 



Average availability — Rubner. 





Availa- 
bility. 


Specific 
dynamic 
effect. 


Body protein 


Per cent. 
68.1 

72! 

87.3 
94.2 


Per cent. 
31.9 
30.9 
28.0 
12.7 
5.8 


Meat protein 


Gelatin 


Fat 


Cane sugar 





CAUSES OF INCREASED METABOLISM. 

The foregoing paragraphs have dealt with the fact of the in- 
creased metabolism and consequent heat production resulting from 
the ingestion of feed without considering the cause of the increase. 
Two explanations of it naturally suggest themselves. The first is 
that the greater supply of the various nutrients directly stimulates 
the metabolism of the body cells, while the second ascribes the in- 
creased metabolism to the additional expenditure of energy required 
for the digestion of the feed and its preparation for metabolism in 
the actual vital processes. The latter explanation is the one which 
has been generally accepted, although by no means without dissent, 1 



1 Compare Heilner, Zeitschrift fiir Biologie, vol. 48, p. 144 ; vol. 50, p. 488. 



CAUSES OF INCREASED METABOLISM. 29 

and the expenditure of energy for these purposes has been somewhat 
loosely and perhaps not altogether fortunately designated as the 
" work of digestion." A consideration of some of the processes con- 
nected with the consumption of feed which lead to the liberation 
of energy may serve to clarify the conception. 

MECHANICAL WORK. 

Digestion requires more or less mechanical work in the prehension and 
mastication of the feed and in moving it through the digestive organs. In this 
connection, too, it should be remembered that the feed in this sense includes 
the water as well, three or four parts of water being usually consumed by 
herbivora for each part of dry matter in the feed. As noted on p. — , Zuntz 
and Hagemann have compared the metabolism of the horse while eating with 
that of the same animal while at rest and computed from the difference the 
amount of energy expended in mastication. The following recapitulation of 
some of their results shows the number of calories of energy expended in the 
mastication of 1 kilogram of the material named : 

Calories. 



Hay 167.5 

Green alfalfa 30.4 

Oats 47. 

Maize 13. 8 



Kellner 1 has investigated the effect of the grinding of straw upon its value 
in a productive ration. He finds that, the practical elimination in this way of 
the work of mastication reduces the expenditure of energy by approximately 
0.66 calorie for each gram of crude fiber present in the straw. 

That the movement of the masticated feed through the digestive tract must 
also require an expenditure of energy is obvious, but no data are available 
as to its amount. 

SECRETION. 

The secretion of the digestive fluids likewise requires some expenditure of 
energy. This has been shown by direct experiment to be true of the salivary 
glands and the pancreas and is also true, doubtless, of the other digestive 
glands. Apparently, however, the amounts of energy thus expended are com- 
paratively small. 

FERMENTATION. 

The extensive fermentations occurring in the digestive tract of herbivora 
result in a considerable evolution of heat. The most important of these is the 
methane fermentation. Assuming on the basis of Tappeiner's results 2 that 100 
grams of carbohydrates yield 4.7 grams of methane and 33.5 grams of carbon 
dioxid, and assuming further that two-thirds of the carbon of the organic 
acids produced is contained in acetic acid and the remainder in butyric, it may 
be computed that the heat evolved amounts to 12.5 per cent of the total energy 
of the digested carbohydrates or 0.523 calorie per gram. It should be noted 
that this estimate does not refer to the potential energy carried off in the 
methane, but to the heat evolved in the fermentation. The latter is part of 
the metabolizable energy of the carbohydrates, since it is liberated in the 



1 Die Ernahrung der Landwirtschaftliehe Nutztiere, 5th ed., p. 163. 
2Zeitschrift fur Biologie, vol. 20, p. 52. 



30 



MAINTENANCE RATIONS OF EAEM ANIMALS. 



kinetic form in the body, but since it takes at once the form of heat, it is not 
available energy in the sense in which the term is here used, 
v The same general considerations, of course, apply to the other fermentations 
and putrefactions which occur in the digestive tract, but their amount in 
herbivora is probably small compared with that of the methane fermentation, 
and we have relatively little knowledge regarding them. 

DIGESTIVE CLEAVAGES. 

It is well known that extensive cleavages of the feed ingredients occur in the 
digestive tract. The nutrients, by the action of the digestive ferments, are split 
up into simpler atomic groupings — the so-called building stones of the mole- 
cule — out of which the proteins, carbohydrates, and fats peculiar to the animal 
body are built up. One argument which has been brought forward in the past 
against the extensive occurrence of such cleavages in natural digestion, espe- 
cially of the proteins, has been the teleological one that the splitting up into 
these comparatively simple compounds was a waste of valuable nutritive mate- 
rial. On the other hand these processes have been invoked to explain the 
striking effect of the proteins in stimulating the metabolism — their large specific 
dynamic effect, to use Rubner's terminology. So far as the peculiar use of pro- 
tein in the body is concerned, it is well established that its crystalline cleavage 
products can be resynthesized to form protein. It is of special interest, there- 
fore, to learn that these cleavages and resyntheses are apparently nearly isother- 
mic processes. Some of the cleavage products of protein contain more potential 
energy per gram than protein itself, as, for example, leucin, with 6.525 calories 
per gram, and tyrosin, with 5.916 calories per gram. Others, like alanin, with 
a heat of combustion of 4.356 calories, contain but little less energy than the 
protein from which they are derived. Even the simplest amino-acid, glycocol, 
resulting from this cleavage has a heat of combustion of 3.129 calories per 
gram. The impression which these figures give — that but little energy is lost 
in the cleavage of the proteins — is confirmed by direct experiments. Loewi 1 
found the dry residue of the tryptic digestion of meat to have an energy value of 
4.6 calories per gram. Tangl, Lengyel, and Hari 2 found the products of the 
peptic or tryptic digestion of egg albumin and serum albumin to contain nearly 
or quite as much potential energy as the original protein. Grafe 3 has made arti- 
ficial digestions of protein in a calorimeter, and found no noticeable evolution 
or absorption of heat. It seems safe, therefore, to regard the digestive cleavage 
of protein as at least a nearly isothermic process, causing little loss of energy in 
digestion. 

Substantially the same thing is true of the digestive cleavage of carbohy- 
drates and fats. Thus 1 gram of starch yields 1.111 grams of dextrose, and 
the heats of combustion of these quantities are, respectively, 4.183 calories and 
4.159 calories, showing a loss of less than 0.6 per cent. One gram of sucrose 
yields 0.5264 gram each of dextrose and levulose, and the energy values are, 
respectively, 3.955 calories and 3.947 calories, or a loss of less than 0.2 per cent 
So, too, 1 gram of tristearin with a heat of combustion of 9.43 calories yields 
by hydrolysis 0.9573 gram of stearic acid, equivalent to 9.026 calories, and 
0.1033 gram of glycerin, equivalent to 0.424 calorie, or a total of 9.45 calories. 

1 Leathes. Problems in Animal Metabolism, p. 129. 

2 Archiv fur die gesammte Physiologie des Menschen und der Thiere (Pfliiger), vol. 
115, p. 1. 

3 .Tahresbericht Tiber die Fortschritte der Tier Chemie, vol. 37, p. 917. 



CAUSES OF INCREASED METABOLISM. 



31 



INTERMEDIARY METABOLISM. 

The chemical reactions taking place during the so-called intermediary metabo- 
lism of the resorbed material before it is finally utilized for the vital processes 
have also to be considered as possible sources of heat production, although our 
present knowledge of them is meager. 

This possibility is of special interest in connection with the marked effect of 
protein on the energy metabolism, since this can hardly be ascribed to digestive 
work in the strict sense. In the normal digestion of protein fermentations play 
a very small part, while, as just shown, the digestive cleavage of protein is 
substantially isothermic. Neither can we imagine that the mechanical work 
of digestion or the secretion of digestive juices can account for the large 
expenditure of energy. Rubner 1 has reported experiments in which the protein 
katabolism of the fasting animal was artificially increased by the administra- 
tion of phlorhizin, and in which a similar increase in the heat production is 
computed, although there could have been no digestive work in the strict sense. 
Falta, Grote, and Stahlein 2 have found that the products of the tryptic diges- 
tion of casein when fed to a dog produce nearly as great an increase in the 
metabolism as does a corresponding amount of casein, while in the familiar 
experiments of Zuntz and Mering 3 the intravenous injection of the crude prod- 
ucts of the peptic digestion of blood fibrin had a like effect. 

The katabolism of protein seems to consist in outline, first, of a hydrolytic 
cleavage into peptids and amino-acids and, second, in a deamidization of these 
latter compounds, and it is the nonnitrogenous products resulting from this 
deamidization which serve as a source of energy for the body, the nitrogen 
being split off as ammonia and excreted as urea. It is to a liberation of 
energy in the form of heat in these preliminary processes of preparing protein 
to serve as fuel that Rubner and other authors ascribe its specific dynamic 
effect. 

Our knowledge of the intermediary metabolism of protein is too meager to 
render any quantitative estimate of the amount of energy lost in this way of 
much value. The cleavage of protein, as noted, seems to be substantially iso- 
thermic. The deamidization of the simpler amino-acids with a small number 
of carbon atoms seems at first thought to involve considerable loss of energy. 
For example, the potential energy of 1 gram of glycocol and of alanin and of 
equivalent amounts of acetic and propionic acids are: 



Glycocol. 



Alanin. 



Energy of amino acid 

Energy of equivalent fatty acid 

Difference 

Percentage loss 



Calories. 
3.129 
2.791 



Calories. 
4.356 
4. 129 



10.! 



.338 



.227 
5.2 



A similar comparison of alanin with the equivalent amount of lactic acid 
shows an apparent loss of about 14 per cent. With the higher members of the 
series, the loss computed in this way is relatively small. It must be remem- 
bered, however, that the amino group is split off as ammonia, which also con- 

1 Gesetze des Energieverbrauchs bei der Ernahrung. 

2 Beitrage zur Chemischen Physiologie und Pathologie, vol. 9, p. 372. 

3 Archiv fur die gesammte Physiologie des Menschen und der Thiere (Pfliiger), vol. 32, 
p. 199, 



32 



MAINTENANCE KATIONS OF FARM ANIMALS. 



tains potential energy equal, according to Ostwald, to 3.319 calories per gram 
in the gaseous state. If we assume that the alanin yields lactic acid with a 
heat of combustion of 3.7 calories per gram we may make the following com- 
parison : 

Calories. Calories. 

Energy of 1 gram alanin 4. 356 

Energy of 1. Oil grams lactic acid 3. 742 

Energy of 0. 191 gram ammonia 0. 634 

4.376 



Difference . 020 

In other words, it would appear that the deamidization of the amino acids, 
like the antecedent cleavage of the proteins, is a nearly isothermic reaction and 
that we must seek elsewhere for the explanation of the specific dynamic effect 
of protein. We can by no means assert, however, that the protein katabolism 
actually takes place according to this simple scheme, nor that the nonnitrog- 
enous substances resulting from deamidization of the amino acids yield their 
energy without loss. It seems not unlikely that the higher fatty acids and other 
nonnitrogenous derivatives of protein are broken down by cleavage and other- 
wise to comparatively simple molecules before they are finally oxidized, and 
there is the possibility of more or less loss of energy in such processes. 

As already indicated, Rubner explains the specific dynamic effect of protein 
from the foregoing point of view, but in a different manner. It has been shown 
beyond reasonable doubt that sugar is produced, or may be produced, in the 
katabolism of protein. According to Rubner, it is only the energy of this sugar 
that is capable of being used for the physiological functions of the body cells, 
while the energy set free in the conversion of protein into sugar is liberated as 
heat and constitutes the specific dynamic effect. This explanation of Rubner's, 
however, seems to be disproved by recent results reported by Lusk and Ringer. 1 
They have shown that alanin is completely convertible to dextrose in a diabetic 
animal, while in the case of glutamic acid but three out of the five carbon atoms 
of the molecule are utilized for the production of dextrose. According to Rub- 
ner's hypothesis, therefore, alanin should show no specific dynamic effect, while 
glutamic acid should show a considerable one. In a preliminary communication 
Lusk 2 reports that neither one of these amino acids when added to a standard 
diet increased the excretion of carbon dioxid in the respiration. This result is 
in striking contrast with those of Falta, Grote, and Sttihlein and of Zuntz and 
Mering just referred to, in which the crude products of tryptic or peptic diges- 
tion were fed. They suggest that some substance other than the recognized 
ammo-acids may be responsible for the stimulating effect of protein upon metabo- 
lism, while they likewise recall the fact that crude peptones have been found to 
have a poisonous effect when injected intravenously while purified peptones do 
not, and likewise the fact that in Zuntz and Mering's experiments purified 
peptones caused no increase in the metabolism. 

EXCRETION. 

Zuntz 3 calls attention to Barcrof t's 4 experiments, which show that the excre- 
tory activity of the kidneys is accompanied by a notable increase in the 
amount of oxygen consumed, and sees in the work thrown on these organs 
by the elimination of the nitrogen of protein one of the causes of its specific 

1 Journal of the American Chemical Society, vol. 32, p. G71. 

2 Proceedings of Society for Experimental Biology and Medicine, 1910, vol. 7, p. 136. 
■■ Medizinsche Klinik. 1910. 

* Ergebnisse der Physiologie, vol. 7, p. 744. 



THE MAINTENANCE EATION. 



33 



dynamic effect. In experiments in collaboration with Steck he found that 
a marked increase of the metabolism, as computed from the oxygen consumed, 
followed the administration of urea, and likewise of sodium chlorid, to 
men and dogs. In the case of urea he computes that the effect was equal to 
20 to 25 per cent of that of an equivalent amount of protein. Zuntz also calls 
attention to earlier experiments by Nering and Schmoll in which carbo- 
hydrates added to the diet of a diabetic produced a similar increase of metab- 
olism, although the sugar was not assimilated but excreted unchanged. Zuntz 
ascribes the results obtained by Rubner to the fact that phlorhizin added largely 
to the increased excretory work required by the elimination of the nitrogen and 
of the sugar formed, pointing out also that Rubner has overestimated the 
amount of heat produced through failure to deduct the energy of the sugar ex- 
creted in the urine. On the other hand, in Lusk's experiments, just quoted, 
there was an increased excretion of urea subsequent to the administration of 
amino acids, but no increase in the carbon dioxide excreted, while Tangl 1 finds 
that the intravenous injection of urea or sodium chlorid causes an increase in 
the metabolism even when the kidneys have been extirpated or clamped off. 

On the whole, it can not be said that any fully satisfactory explana- 
tion has yet been offered of the effects of feed, and in particular of 
protein, upon the metabolism, although certain factors, especially in 
domestic animals, are clearly evident. 

But whatever explanation we may accept — whether, following 
Zuntz, we speak of work of digestion, or, with Rubner, avoid any 
implication as to the cause by the use of the term specific dynamic 
effect — the fact that the metabolizable energy of different feeding 
substances is not equally available for maintenance is established 
beyond question, and it is this fact which is of immediate importance 
in considering the energy requirement for maintenance and the main- 
tenance values of feeding stuffs. 

THE MAINTENANCE RATION. 

In accordance with the principles laid down in the foregoing para- 
graphs, a maintenance ration as regards energy may be defined as 
one which supplies available energy equal to the fasting katabolism. 

For example, in Rubner's experiment cited on page 27, in which 
fat was fed, the fasting katabolism of the dog was 54 calories per 
kilogram. Fat containing 53.4 calories of metabolizable energy di- 
minished the loss of body tissue by 46.5 calories. Evidently, then, 
to reduce the loss by 54 calories, that is, to reduce it to zero, would 
have required 53.4X^6 — ^2 calories of metabolizable energy to 
be supplied in fat. The same thing may also be expressed in a 
slightly different wa}< : If, as there computed, only 87.08 per cent of 
the metabolizable energy of fat is available, then to make good a total 
loss of 54 calories will require 54-f-0.8708=62 calories of metaboliza- 



1 Biochemische Zeitschrift, vol. 34, p. 1. 
8489°— Bull. 143—12 3 



34 



MAINTENANCE EATIONS OF FARM ANIMALS. 



ble energy in fat. 1 On this basis we may compute from Rubner's 
final averages (p. 28) that to maintain the dog experimented on, 
that is, to make good the loss of 54 calories of energy per kilogram, 
it would haA T e been necessary to supply per kilogram the following 
amounts of metabolizable energy in the materials named : 

Calories. 

In meat protein 79. 3 

In gelatin 78. 1 

In fat 61.9 

In cane sugar 57. 3 

These figures afford a simple illustration of the fact that the amount 
of metabolizable energy required for maintenance is variable, being 
greater as its availability is less. The maintenance requirement of 
the dog was 54 calories of available energy. The maintenance ration 
needed to supply this varied according to the material which served 
as the carrier of the energy. 

The same relations hold good for farm animals, although the fact 
that we can not well observe their fasting katabolism directly makes 
the computation a trifle more complicated. As an example, we may 
take the experiment on timothy hay already cited on page 20. The 
addition of 2.1 kilograms of timothy hay, equivalent to 3.575 therms 
of metabolizable energy, to the basal ration reduced the loss of energy 
from the body of the animal by 2.020 therms. Evidently, then, to 
have reduced it by 2.377 therms, that is, to zero, would have required 
2 377 

the addition of 2.1 X ' ft9n = 2.471 kilograms of the hay, equivalent 

to 4.207 therms of metabolizable energy. The total maintenance ration 
of this particular feeding stuff, then, would have been the basal 
ration plus this amount, or 5,670 kilograms of the hay, equivalent to 
9.894 therms of metabolizable energy. 

The same result may also be obtained by the use of the percentage 
availability as computed, viz, 56.5 per cent. The heavier ration 
failed to maintain the animal by 0.357 therms, that is, it lacked this 
amount of available energy. To supply this requirement would evi- 
dently demand 0.357^-0.565=0.632 therms of metabolizable energy, 
which added to the 9.262 therms already contained in the ration 
gives a total as above of 9.894 therms. The same computation can, 
of course, be made from the lighter ration with the same result. 

From the data given it is likewise possible to compute what the loss 
by the body would have been had it been practicable to withdraw all 
feed. The basal ration contained 5.687 therms of metabolizable 
energy, of which 56.5 per cent was available ; that is, the basal ration 
was capable of preventing the loss of 5.687X0.565=3.213 therms from 

1 On the assumption, of course, that the effect is a linear function of the amount of 
food. 



THE MAINTENANCE EATION. 



35 



the body. Had the basal ration been entirely withdrawn, then the 
loss would have been increased by this amount ; that is, the total loss 
would have been 3.213+2.377=5.590 therms. The same quantity 
would, of course, be obtained by starting- from the heavier ration 
or from the maintenance ration as computed above. The fasting 
katabolism, which can not well be determined directly, is thus ob- 
tained by computation. In other words, this steer expended daily 
5.590 therms of energy in the maintenance of his necessary vital proc- 
esses aside from those connected with the digestion and assimilation 
of his feed. This was his maintenance requirement as denned in the 
foregoing paragraphs, and an amount of the clover hay which was 
capable of supplying this quantity of available energy, viz, 5.670 
kilograms, was a maintenance ration, while on smaller amounts he 
drew upon his body tissues to cover the deficiency. 



£ 
















4 







Fig. 1. — Availability of metabolizable energy of hay. 



All these facts maj^ also be conveniently represented graphically 
as follows : 

If on the two coordinate axes of figure 1, we let the horizontal distances 
represent the metabolizable energy of the feed and the vertical distances the 
gain of energy by the body of the animal, the results of the two experiments just 
referred to may be represented by the points A and B, the distances OE (equal 
to 5.687 therms) and OF (equal to 9.262 therms) representing the amounts of 
metabolizable energy in the two rations and the distances EA (equal to 
—2.377 therms) and EB (equal to —0.357 therm) the corresponding (negative) 
gains of energy by the animal. A straight line drawn through A and B and in- 
tersecting the two axes at D and C will then represent the relation between the 
supply of metabolizable energy in the feed and the grain by the body of the 
animal. 1 This relation may also be expressed analytically by the equation 
y=ax — m, in which m=OD (equal to 5.590 therms) will represent the com- 



1 Assuming that this is a linear function. 



36 



MAINTENANCE RATIONS OF FARM ANIMALS. 



puted fasting katabolisui and a the tangent of the angle between AB and the 
horizontal axis (equaling in this case 0.565), or the percentage availability, 
while OC (equal to 9.S94 therms) is the maintenance ration in terms of the 
metabolizable energy of this particular hay. 

The fasting katabolism being a constant quantity under like con- 
ditions, it follows that an amount of any feed capable of supplying 
5.590 therms of available energy would have been a maintenance 
ration for this animal. It is clear then that the actual weight of 
feed required for maintenance will vary inversely as the availabil- 
ity of its energy. With this particular hay, it would have been nec- 
essaiw to use an amount containing 9.894 therms of metabolizable 
energy. With the timothy hay used in an earlier experiment, how- 
ever, 62.9 per cent of whose metabolizable energy was found to be 
available, corresponding to the line DG in figure 1, it would have 
been necessary to use a quantity containing only 5.590-f-0.629= 
8.888 therms, represented in the figure by OG, in order to supply 
the requisite available energy and secure maintenance. On the other 
hand, with a coarser forage having, e. g., an availability of only 
45 per cent, represented b}^ DH, it would have been necessary to 
supply 5.590-1-0.45== 12.420 therms of metabolizable energy, repre- 
sented in the figure b}^ the line OH. Just as was illustrated pre- 
viously in the case of the dog, while the real requirement of energ}' 
for the vital processes remains unchanged the amount of feed nec- 
essary for maintenance is variable, depending upon the availability 
of its energy. 

If with Zuntz we regard the increased katabolism consequent 
upon taking feed as representing energy expended in its digestion 
and assimilation, we may state the case in a slightly different way. 
We may compare the work thus done to the work of placing the fuel 
under a factory boiler. If this is done by means of power derived 
from the same boiler, it is evident that the farther the fuel has to 
be moved and the greater the amount of incombustible waste which 
it contains, the larger will be the fraction of the total boiler power 
required simply to keep the fire going and the less the proportion 
available for running the factory. So in the body, the greater the 
amount of energy which must be expended on the food in order to 
prepare it for its functions in the body the less is the proportion of 
its energy which is available for carrying on the physiological 
processes. 

RELATION OF MAINTENANCE REQUIREMENT TO LIVE WEIGHT. 

Before taking up the specific maintenance requirements of farm 
animals, it is necessary to consider the influence of size and weight 
upon the maintenance requirement. 



RELATION OF MAINTENANCE TO LIVE WEIGHT. 



37 



That large animals katabolize more matter and produce more heat 
than smaller ones requires no special proof. Experiment shows, 
however, that the difference is not proportional to size or weight, 
but that small animals have a relatively more intense metabolism 
than large ones, the amount being approximately proportional to the 
body surface, which, of course, is relatively greater in the smaller 
animal. The existence of such a relation was surmised by various 
writers, but we are indebted to Rubner 1 for the first quantitative 
investigation of this question. He determined the fasting katabolism 
of six clogs whose weights ranged from 3 to 24 kilograms. With 
the addition of earlier experiments by Voit on a still larger dog, 
the average results were as follows, the total katabolism being ex- 
pressed in terms of computed energy. 

Relation of fasting katabolism to weight and to surface — Rwbner and Voir. 



No. of animal. 




Katabolism Katabolism 
per kilo- 

gram, live Xrtv 



I. .. 

II. . 
III. 
IV. 

v.. 

VI. 
VII 



Calories. 
36. 66 
40.91 
45.87 
46.20 
65.16 
64.79 
88.25 



Calories. 
1,046 
1,112 
1,207 
1,097 
1,183 
1.120 
1,214 



While not mathematically constant, the ratio between the fasting 
katabolism and the surface shows a close approximation to uni- 
formity, and the same fact has been verified by a considerable num- 
ber of subsequent experiments. Moreover, it has been shown 2 to 
be approximately true not only of animals of the same species, but of 
animals ranging in size from man to domestic fowls, and including 
also cold-blooded animals. A recent investigation by Kettner 3 upon 
13 guinea pigs furnishes a striking illustration of this general uni- 
formity. 

Rubner explains the apparent dependence of the fasting katabolism 
on body surface as the consequence of the loss of heat from the body 
due to the cooling action of the environment, which would naturally 
be proportional to the surface. The fact, however, that not incon- 
siderable variations have sometimes been observed indicates that 
other factors than the elimination of heat are concerned, and appar- 
ently the true cause lies deeper. Not merely the heat production but 
all the important physiological activities of the body, including the 
expenditure of energy in locomotion, seem to be proportional to the 



1 Zeitschrift fur Biologie, vol. 19, p. 535. 

2 E. Voit. Zeitschrift fur Biologie, vol. 41, p. 113. 

3 Archiv fur (Anatomie und) Physiologie, 1909, p. 447. 



38 



MAINTENANCE RATIONS OF FARM ANIMALS. 



body surface rather than to the weight, while the fact that the same 
law holds true for cold-blooded animals, which assume the tempera- 
ture of their surroundings and which, therefore, are subjected to no 
demand for heat, points in the same direction. Apparently we have 
here a general biological law of which the proportionality between 
heat production and body surface is one expression. 

The internal work of the animal, however, as measured by the fast- 
ing katabolism or the fasting heat production, constitutes, as we have 
seen, its maintenance requirement. The maintenance requirements of 
animals of different sizes, therefore, especially of those of the same 
species, are proportional to their surfaces. 

COMPUTATION OF RELATIVE BODY SURFACE. 

Few actual determinations of the body surface of animals have 
been made and almost none for farm animals, so that it is at present 
impossible to express with accuracy the metabolism of the latter 
animals per unit of surface. For purposes of comparison between 
individuals of the same species, however, another method serves to 
give at least approximate results. It is a familiar geometrical fact 
that the surfaces of two solids of the same shape (i. e., similar figures 
in the geometrical sense) are proportional to the two-thirds powers 
of their volumes. By regarding all animals of the same species as 
of the same shape and also as having the same specific gravit}^, so 
that their weights are proportional to their volumes, it is a very 
simple matter to compute their relative surfaces and the correspond- 
ing maintenance requirements. For example, a steer weighing 583 
kilograms was found to have a computed fasting katabolism (i. e., 
maintenance requirement) of 8.671 therms. A steer weighing 500 
kilograms, other things being equal, would have a maintenance re- 
quirement in proportion to its smaller surface. The latter would be 
to the surface of the larger animal, approximately, as (500) ^ is to 
(583) § and the maintenance requirement would therefore be 8.671 

X^|^^ 8 = 7.878 therms. In this way it is a simple matter to com- 
pute the relative maintenance requirements of different individuals 
without the necessity of expressing them per unit of surface. 

Of course, such a comparison is only approximately correct. In 
the first place, it may be presumed that there are differences in the 
specific gravity of different individuals, although it may be doubted 
whether these differences are sufficiently great to be of much sig- 
nificance in this connection. Moreover, different animals are not of 
the same shape. The young animal differs in conformation from the 
older one, and the beef steer and the dairy cow, for example, are far 
from being geometrically similar. It would be of much interest to 
determine the relation of surface to weight in different species, types, 
and ages of domestic animals, but lacking such determinations the 



MAINTENANCE EATIONS OF CATTLE. 



39 



method of computation above outlined may probably be assumed to 
give a fair approach to the truth and is at any rate the only one 
available. 

THE MAINTENANCE EATIONS OF FARM ANIMALS. 

In endeavoring to formulate the maintenance rations of farm 
animals it is important to have a clear conception of the nature of 
the problem and to distinguish between its physiological and its 
economic aspects. The physiological conception of the maintenance 
requirement is the amount of energy required to carry on the abso- 
lutely necessary vital processes in a state of the most complete rest 
possible. It is the least amount on which life can be sustained; 
the physiological minimum ; the base line for comparison. In actual 
practice, no such state of complete rest can be maintained for any 
length of time. There is necessarily superadded to the minimum 
physiological requirement the energy expended in a variety of ways, 
but especially in the numerous minor muscular movements which are 
unavoidable in the waking state, which may be summarized under 
the term incidental work. Some of the factors of this incidental 
work are discussed on subsequent pages. Physiologically, this addi- 
tional energy is expended for production; the animal is doing work 
on its surroundings. Economically, however, the work done is of 
no value and the energy required to do it is, therefore, from that 
point of view, a part of the cost of maintenance. In practice, of 
course, it is not the physiological but the economic requirement which 
is of importance. The latter will neeessarity be more or less variable 
according to the individuality of the animal and the conditions 
under which it is maintained, as will appear in the following dis- 
cussion, and statements of maintenance requirements and rations 
should therefore indicate to such a degree as is possible the conditions 
to which they are intended to apply. 

CATTLE. 

The maintenance requirements of cattle have been more exten- 
sively studied than those of other species and it will be convenient 
to take them up first, using the data also as a means of illustrating 
the principles involved and the methods of investigation employed. 

The estimate of the maintenance ration of cattle long current 
and still occasionally cited was based upon the investigations of 
Henneberg and Stohmann 1 in 1858. According to their results, a 
1,000-pound steer required for maintenance about 8.16 pounds of 
digestible organic matter per day, equivalent to about 14.3 therms 
of metabolizable energy. In view of the rather high stable tem- 

1 Beitriige zur Begriindung einer i"ationellen Futterung der Wiederkauer, Heft I, 
pp. 17-188. 



40 



MAINTENANCE RATIONS OF FARM ANIMALS. 



perature in these experiments, however, Wolff 1 when formulating 
his well-known feeding standards increased this amount to 9.1 pounds 
digestible organic matter, equivalent to about 15.9 therms of meta- 
bolizable energy. Numerous subsequent experiments, 2 however, 
showed quite clearly that this estimate was considerably too high 
but without affording a sufficient basis for its correction, and it is 
only since 1898 that really satisfactory data have been secured. 

One general method of experimentation has already been illus- 
trated in the computation on pages 34-35 of the maintenance require- 
ment of a steer. In brief, it consists of comparing the losses of body 
energy by the animal when fed two different amounts of the same 
feed or combination of feeds, each being less than the maintenance 
ration, and computing from the difference the amount of energy 
required for simple maintenance. 

Investigations by Arrusby and Fries 3 include eight trials with three different 
animals substantially upon this plan. In the later experiments of the series 
a correction was made for differences in live weight in the different periods 
of each experiment and for differences in the amount of time spent standing 
and lying, the results being computed to 12 hours standing. The results here 
given for the earlier experiments have been corrected in the same manner 
and therefore differ somewhat from those originally reported. The follow- 
ing tabulation of the results shows also, for comparison, the percentage avail- 
ability of the metabolizable energy of the feed and likewise the maintenance 
ration expressed in terms of metabolizable energy. The results in every case 
have been computed to a uniform live weight in proportion to the two-thirds 
power of the weight. It is to be noted that the experiments are upon coarse 
fodder (clover and timothy hay) exclusively, and that the animals were not fat. 



Maintenance requirements and rations of steers — Armsby and Fries. 



Years. 


Animal. 


Available energy 
for maintenance. 


Percent- 
age 
availa- 
bility of 
metabo- 
lizable 
energy. 


Metabolizable en- 
ergy for main- 
tenance. 


Feed. 


Per 500 
kilograms 
live 
weight. 


Per 1,000 
pounds 

live 
weight. 


Per 500 
kilograms 
live 
weight. 


Per 1,000 
pounds 

live 
weight. 


1903 

1904 

1905 

1906 

1906 

1907 

1907 

Average of all 

Average, omitting 
1904. 

Average, 1905-1907 


i 

A 
B 
A 
B 
A 
B 


Therms. 
6. 483 
7.812 
6. 649 
7.532 
6. 077 
6. 806 
5.186 
6. 931 


Therms. 
6. 076 
7.321 
6.231 
7.058 
5.695 
6.378 
4. 860 
6. 496 


Per cent. 
50.88 
80. 24 
60.51 
55.21 
[57.05] 
[56. 50] 
57.05 
56. 50 


Therms. 
12.742 

9.736 
10.988 
13. 642 
10. 652 
12. 046 

9.090 
12. 267 


Therms. 
11.942 

9.124 
10. 297 
12. 784 

9.982 
11.288 

8. 519 
11. 497 


Clover hay. 
Do. 

Timothy hay. 
Do. 
Do. 
Do. 
Do. 
Do. 


6. 685 
6.523 

6. 531 


6. 2G4 
6.113 

6.121 


59.24 
56.24 

57.14 


11.395 
11. 632 

11. 447 


10. 679 
10. 901 

10.728 



1 Landwirtschaftliche Fiittorun^slchre, 2d ed., 1877, pp. 132 and 196. 

2 The Maintenance Ration of Cattle, Pennsylvania Experiment Station Bulletin 42, 
pp. 12-21. 

8 Bureau of Animal Industry, Bulletins 74, 101, and 128. The results reported in 
Bulletin No. 51 can not be computed directly in this way because the ration included a; 
small fixed amount of linseed meal. 



MAINTENANCE RATIONS OF CATTLE. 



41 



Omitting the results of the year 1904, which are obviously too high both as 
regards the maintenance requirement and the percentage availability, we ob- 
tain the following averages in round numbers : 





Available 


Metaboliz- 
able 




energy. 


energy. 




Therms. 


Therms. 


Per 500 kilograms live weight 


6. 52 


11.63 


Per 1,000 pounds live weight 


G.ll 


10.90 



The variations from these averages which occur in individual cases illus- 
trate the fact, already pointed out, that the economic as distinguished from 
the physiological requirement may vary considerably with different animals 
and under different conditions. 

The experiments just cited are the only ones thus far reported in 
which this precise method of determining the maintenance require- 
ment in terms of available energy has been followed. In the major- 
ity of investigations the effort has been to feed as nearly an exact 
maintenance ration as possible, making a correction for the small 
gains or losses by the animals, and the results of these experiments 
have usually been expressed in terms of metabolizable energy. 

By far the most exact and satisfactory experiments of this sort, as well as 
the earliest, are those reported by Kellner from the Moeckern Experiment 
Station 1 in 1894 and 1896, in which the gain or loss of protein and fat (nitro- 
gen and carbon balances) was determined by means of a Pettenkofer respira- 
tion apparatus. In these experiments the feed consisted exclusively of coarse 
fodder, viz, meadow hay, or, in two instances, a mixture of clover hay and 
oat straw. In six cases out of the eight the respiration experiments showed a 
small gain of protein and fat by the animal ; that is, the ration was somewhat 
above the maintenance requirement. For example, the gains by ox A on meadow 
hay and the computed equivalent amounts of energy were : 





Material 
gained. 


Equivalent 
energy. 


Protein 


Grams. 
37.2 
140.8 


Therms. 
0. 211 
1.338 

1.549 


Fat 


Total 







In later investigations by Kellner, out of 100 units of metabolizable energy 
of meadow hay supplied in excess of the maintenance requirement, only 43 
were recovered in the protein and fat gained by the body. To produce the gain 
observed in this experiment, therefore, may be computed to have required 
1.549-K).43 =3.602 therms of metabolizable energy and the ration must have con- 
tained this amount in excess of the maintenance ration. The following calcu- 

1 Die Landwirtschaftlichen Versuchs-Stationen, vol. 44, p. 370; vol. 47, p. 310; vol. 53, 
pp. 6-16. 



42 



MAINTENANCE RATIONS OF FARM ANIMALS. 



latiou. therefore, shows the amount of nietabolizable energy of meadow hay 
which was necessary for the maintenance of the animal : 



Therms. 

Energy of feed 32. 177 

Energy of feces 11. 750 

Energy of urin 1. 945 

Energy of methane 2. 114 

Energy of total excreta ■ 15.809 



Metabolizable energy of ration 16.368 

Metabolizable energy equivalent to gain 3. 602 



Metabolizable energy for maintenance 12. 766 



This method of computing the metabolizable energy necessary for maintenance 
is obviously the same in principle as that employed in Arinsby and Fries' s 
experiments, differing only in the fact that the comparison is made on amounts 
of feed exceeding the maintenance ration. Kellner's results, however, can not 
be made the basis of a direct computation of the available energy required for 
maintenance, since it appears probable that a larger percentage of the energy 
of hay is available below the point of maintenance than is utilized for gain 
above it. 1 

In two cases (ox B and ox IV) the rations were less than the maintenance 
ration and the animals lost more or less protein and fat. In computing 
these experiments Kellner, in accordance with the ideas then generally ac- 
cepted, simply added the energy equivalent to the loss of tissue to the total 
metabolizable energy of the feed to obtain the maintenance ration. It is evi- 
dent, however, from what has subsequently been learned regarding the avail- 
ability of metabolizable energy, as outlined in the foregoing paragraphs, that 
if, for example, ox B lost tissue equivalent to 1.498 therms it would have 
required more than this amount of metabolizable energy in the food to make 
good the loss, the quantity necessary depending upon the availability of the 
energy. Of the latter we have no determinations for this particular ration, but 
for purposes of computing a correction we may, perhaps, assume it to be the 
same as that found by Armsby and Fries for timothy hay, viz, about 57 per 
cent. On this assumption the equivalent amount of metabolizable energy which 
would have had to be supplied to reach the maintenance ration of ox B 
would have been 1.498^-0.57=2.628 therms, a difference of 1.130 therms. For ox 
IV the corresponding correction is only 0.740 therm. 

Making these slight changes in Kellner's original figures for these two 
animals for the sake of uniformity, his results are as follows : 



1 Compare Bulletin 128, Bureau of Animal Industry, p. 59. 



MAINTENANCE RATIONS OF CATTLE. 43 



Maintenance rations of oxen — Kcllner. 





Live . 
weight. 


Stable 
tempera- 
ture. 


Maintenance ration 
(metabolizable energy). 


Per head. 


Per 500 
kilograms. 


Per 1,000 
pounds. 


Tallin c\t\ i"ma.lQ * 

Ox V 


Kilos. 
602.' 1 
611.5 
619.8 
622.8 
632.1 
632. 4 
644. 
67L7 


14.7 
15.9 
15.9 
14.9 
14.7 
15.0 
14. 8 
16.' 5 


Therms. 
11. 675 
17. 966 
12. 766 
15. 861 
13.284 
14. 457 
11.771 
15. 213 


Therms. 
10. 316 
15. 709 
11. 060 
13. 701 
11. 352 
12. 3G2 
9. 944 
12.486 


Therms. 

9.668 
14. 721 
10. 365 
12. 840 
10. 639 
11. 585 

9.320 
11. 702 


OxB 


Ox A 


Ox IV 


Ox III 


Ox II 


Ox VI 


Ox XX 




14. 124 
13. 575 


12. 116 
11. 603 


11.355 
10. 874 


Average, omitting ox B 






Fat animals: 

Ox 1 


748.0 
750.0 
858.0 


15.9 
15.2 
16.1 


23.449 
19. 385 
22. 162 


17.93 
14. 79 
15.46 


16.80 
13.86 
14.49 


Ox B 


0x3 

Average 


21. 656 


16. 06 


15.05 









The observed maintenance ration of ox B is notably larger than that of the 
other animals. This animal refused to lie down during the respiration experi- 
ments and presumably, therefore, the result obtained with it is abnormally high. 

Omitting this result, the maximum, minimum, and average maintenance 
rations per 1,000 pounds live weight were : 

Metabolizable energy required for maintenance of cattle per 1,000 pounds live 

weight — Kellner. 



Per 1.000 
pounds 

live 
weight. 



Thin animals: 
Maximum 
Minhnum . 
Average . . 

Fat animals: 
Maximum 
Minimum. 
Average.. 



Therms. 
12.84 
9.32 
10. 87 

16.80 
13.86 
15.05 



If we are justified in assuming, on the basis of Armsby and Fries's results, 
that approximately 57 per cent of the metabolizable energy of these rations 
was available, then the foregoing amounts of metabolizable energy are equiva- 
lent to the following amounts of available energy : 

Computed available energy required for maintenance of cattle — Kellner. 





Per 1,000 
pounds 

live 
weight. 


Per 500 
kilograms 

live 
weight. 


For thin animals : 


Therms. 
7. 32 
5.31 
6. 20 

9. 58 
7. 75 
8. 58 


Therms. 
7.81 
5.67 
6.61 

10.22 
8.42 
9. 15 


Minimum 


Average 


For fat animals: 

Maximum 









44 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Both the averages and the range of the results obtained by Kellner and by 
Armsby and Fries for thin cattle on coarse fodder show a remarkably close 
agreement. The results upon fat cattle will be considered on subsequent pages. 

In addition to the respiration experiments just considered, a num- 
ber of live-weight experiments upon the maintenance ration of cattle 
have been reported. 

Such trials were made by the writer at the Pennsylvania Experiment Sta- 
tion 1 in 1S92 to 1897, the feed being either chiefly or entirely coarse fodder. 
The live weight was taken daily during relatively long periods and the nitrogen 
balance was also determined, and from these data an approximate computation 
of the loss of fat was attempted. The amount of methane excreted, and the 
corresponding loss of metabolizable energy, was calculated from the total carbo- 
hydrates digested. Computing the final results on the same assumptions as in the 
Moeckern experiments, 2 the results of 4 experiments each on 3 animals weighing 
from 400 to 500 kilograms, computed per 500 kilograms live weight, were : 



Metabolizable energy in maintenance rations of steers — Armsby. 





Per 500 kilograms live weight. 


Ration. 










Steer 1. 


Steer 2. 


Steer 3. 


Chiefly or entirely coarse fodder: 


Therms. 


Therms. 


Therms. 


Experiment I, 1892-93 


14. 23 


[17.09] 


13.69 


Experiment II, 1892-1894 


13.61 


13.56 


12. 40 


Experiment VI, 1894-95 


12.92 


12.87 


12.73 


Experiment VII, 1894-95 


13.03 


12.76 


[17-77] 




13.45 


13. 06 


12.94 


Largely grain: 








Experiment VIII 


11.72 


9.15 


10. 70 



Assuming, as before, that about 57 per cent of the metabolizable energy was 
available, and omitting the two apparently exceptional results, the maximum, 
minimum, and average results are: 







Metabolizable energy. 


Available energy. 




Ration. 


Per 500 


Per 1,000 


Per 500 


Per 1,000 






kilograms 


pounds 


kilograms 


pounds 






live weight. 


live weight. 


live weight. 


live weight. 


Coarse fodders: 




Therms. 


Therms. 


Therms. 


Therms. 






14. 23 


13. 34 


8.11 


7.60 


Minimum 




12. 40 


11.62 


7.07 


6.62 




:::. 


13. 15 


12. 32 


7.50 


7.02 


Largely grain 




10. 52 


9:86 


6.00 


5.62 



The results on coarse fodders are materially higher than those of the respira- 
tion experiments just cited, but the method is, of course, much less accurate. 

Haecker 3 reports determinations of the maintenance rations of dry cows made 
in three successive 3^ears and in which three different animals were used. In 
these experiments the nutrients digested were determined directly and the 
sufficiency of the ration judged of from the live weight and appearance of the 
animals. Results obtained by Kellner 4 and by Armsby and Fries 5 show that 

1 Pennsylvania Experiment Station, Bulletin 42. 

2 This differs somewhat from the method of computation followed in the original report 
of the experiments. 

3 Minnesota Experiment Station, Bulletin 70. 

4 Die Landwirtschaftlichon Versuchs-Stalionen, vol. 53, pp. 440-445. 

5 Bureau of Animal Industry, Bulletins 51, 74, 101, and 128. 



MAINTENANCE RATIONS OF CATTLE. 



45 



the lnetabolizable energy does not vary greatly from 1.6 therms per pound (3.5 
therms per kilogram) of total digestible organic matter, even in rations" differing 
widely as to the kinds of feed used. From the data regarding the digestible 
matter of the rations, therefore, the equivalent amounts of metabolizable energy 
may be estimated on this basis. Computing the results per 1,000 pounds in pro- 
portion to the two-thirds power of the live weight, instead of directly as does 
Haecfcer, the results are as follows: 



Maintenance rations of dry cows — Haecker. 



Cow. 


Year. 


Average 

live 
weight. 


Average 
daily gain 
in' live 
weight. 


Kind of feed. 


Metabolizable energy. 


Per head. 


Per 1,000 
pounds live 
weight. 


Alice ■. 


1896-97 
1896-97 


Pounds. 
808 
1,010 


Pound. 






Com fodder 


Therms. 
7. 92 
9. 26 


Therms. 
9. 13 
9. 19 


Belle 




Average 






9. 16 


Belle 


1897-98 

1897- 98 

1898- 99 


1,072 
706 
757 


0. 27 
.27 
. 16 


\ Com fodder, beets, 
/ and oil meal. 
Not stated 




/ 10. 16 
\ 7.01 
8. 96 


9.71 

8.83 
10. 75 


Lottie 


Lottie 


Average 






9. 76 
9.51 


Average of all 

























In the first year's experiments the amount of digestible protein fed was small 
and the condition and appearance of the animals were not satisfactory. In 
the second and third years the rations were richer in protein, a slight gain 
in live weight was made, and the condition of the animals was entirely satis- 
factory at the close of the experiment. Since some gain was made in the 
second and third years the amount consumed was naturally somewhat larger 
than the first year. The proportion of grain to coarse fodder in the rations 
is not stated, but the results of the digestion trials indicate that it must have 
been small. If we assume 60 per cent availability, the computed available 
energy of the rations per 1,000 pounds live weight is : 

Therms. 

Maximum 6. 45 

Minimum 5. 30 

Average of all 5. 71 

The results as thus computed run materially lower than those obtained at 
Moeckern and at the Pennsylvania station, in spite of the fact of a gain in live 
weight. 

Evvard 1 fed three yearling steers for 60 days and one for 362 days on rations 
so adjusted and varied as to very exactly maintain their live weight, the average 
daily gain or loss being practically negligible. The experiment in the case 
of the first three animals followed a 30-day period in which a submaintenance 
ration was fed and the animals were therefore only in medium condition. 2 

The rations fed differed from those of the experiments previously quoted in 
containing a much larger proportion of grain, consisting of 4 parts by weight 
of alfalfa hay and 10 parts of mixed grain. 3 Evvard computes the available 

1 Thesis for degree of M. S., University of Missouri, 1909. 

2 The animals graded in the maintenance period as follows : No. 500, common ; No. 598, 
common ; No. 596, good to medium ; No. 595, medium. 

3 Eight-ninths corn chop and one-ninth old process linseed meal. 



46 



MAINTENANCE EAT IONS OF FAKM ANIMALS. 



energy of tlie rations consumed from the data given in Bulletin 71 of the Penn- 
sylvania station with the following results: 

Maintenance rations of yearling steers — Evvard. (First experiment.) 



No. of 
animal. 


Length 
of experi- 
ment. 


Average 

live 
weight. 


Estimated available 
energy per day. 


Per head. 


Per 1,000 
pounds 1 

live 
weight. 


590 
598 
596 
595 


Days. 
60 
60 
60 
362 


Pounds. 
608 
461 
464 
609 


Therms. 
5.63 
3.85 
4. 34 
5.83 


Therms. 
7. 85 
6.45 
T. 25 
8.09 



1 Computed in proportion to the two-thirds power of the live weight. 



In addition to the uncertainty attaching to such live-weight experiments, as 
well as to the fact that the available energy was estimated, there is also a special 
difficulty in determining the true maintenance requirement of growing animals, 
which will be referred to later. Nevertheless, the results appear to agree fairly 
well with those obtained in the respiration calorimeter experiments. 

The metabolizable energy of the rations, also computed from the data given 
in Bulletin 71 of the Pennsylvania station, is, on the other hand, lower than 
fhat found in either the Pennsylvania or the Moeckern experiments, although 
agreeing well with Haecker's results on dry cows, viz, per 1,000 pounds live 
weight : 

Therms. 

No. 590 10.42 

No. 598 8.57 

No. 596 . 9. 63 

Average 9. 54 

Evvard's first three animals were also fed a maintenance ration of the same 
feeds in the same proportions for 120 days after having been previously fed 
heavier rations for 127 days, during which No. 590 received about one-fourth of 
full feed, No. 598 about one-half, and No. 596 full feed. The results of this 
second maintenance period are summarized in the following table : 



Maintenance rations of yearling steers — Evvard. {Second experiment.) 



No. of 
animal. 


Length 
of experi- 
ment. 


Average 

live 
weight. 


Estimated available 
energy per day. 


Per head. 


Per 1,000 
pounds 

live 
weight. 1 


590 
598 
596 


Days. 
120 
120 
120 


Pounds. 
706 
665 
860 


Therms. 
6. 47 
6.44 
9.66 


Therms. 
8. 15 
8. 45 
10. 62 



i Computed in proportion to the two-thirds power of the live weight. 



MAINTENANCE EATIONS OF CATTLE. 



47 



The data contained in the foregoing pages may be summarized in 
the following table showing the maximum, minimum, and average 
maintenance rations in various experiments. Armsby and Fries's 
results, as already noted, have been corrected to 12 hours standing. 
No statement of the amount of time passed standing and lying, 
respectively, is given in the reports of the other experiments. 

Daily maintenance rations of cattle per 1,000 pounds live weight. 



Investigators. 



Condition 
of animals. 



Num- 
ber of 
ani- 
mals. 



Num- 
ber of 
single 
trials. 



Metabolizable energy. 



Maxi- 
mum. 



Mini- 
mum. 



Aver- 
age. 



Available energy. 



Maxi- 
mum. 



Mini- 
mum. 



Aver- 



Armsby and Fries. . 

Kellner 

Do. 

Armsbv (coarse fod- 
der). 

Armsby (much 
grain). 

Haecker 

Evvard, 60-day ex- 
periment. 

Evvard, 302-day ex- 
periment. 

Evvard, second ex- 
periment. 

Average of all ex- 
periments. 

Average of respira- 
tion experiments. 



Thin 

do... 

Fat 

Thin 

....do... 

....do... 
....do... 



do.... 

Partly fat- 
tened. 

/Thin 

\Fat 

Thin 



Therms. 
12.78 
12. 84 
16.80 
13. 34 

10.98 

10.75 
10. 42 



13. 34 
12.84 



Therms. 
8.52 
9.32 
13. 86 
11.62 

8.57 

8. 83 
8.57 



8.52 



Therms. 
10. 90 
10. 87 
15. 05 
12. 32 

9. 86 

9.51 
9.54 



10.50 
15. 05 
10.89 



Therms. 
7. 06 
7.32 
9. 58 
7.60 

6. 26 

6.45 
7. 85 



10. 62 



7. 32 



Therms. 
4. 86 
5.31 
7. 75 
6. 62 



5. 30 
6. 45 



r. is 



4.86 
"4.86 



Therms. 
6.11 
6.20 
8. 58 
7.02 

5.62 

5.71 
7. 18 



9.07 



6. 31 
8.8S- 
6.16 



The foregoing results justify the statement that the maintenance 
ration of thin cattle, expressed in terms of available energy, ranges 
in general from 5 to 7.5 therms per 1,000 pounds live weight, aver- 
aging a little above 6 therms. The maintenance ration of fat animals 
appears to be distinctly greater than that of thin ones. 

It should be noted that the term available energy is used in the 
sense defined on pages 20-22, as determined by a comparison of ex- 
periments upon submaintenance rations. This available energy is 
not necessarily identical with the energy values in terms of which 
the values of feeding stuffs and the requirements of animals have 
been expressed by Kellner and others (compare Farmers' Bulletin 
346), since his results were obtained by a comparison of super- 
maintenance (productive) rations. Such scanty data as are now on 
record seem to indicate that the two are substantially the same in 
case of concentrated feeds, but that the available energy of coarse 
feeds below maintenance may be greater than their productive values 
above the point of maintenance. If this should prove to be the case, 
then evidently an estimated requirement of 6 therms of Kellner's pro- 
duction values will give a maintenance ration ample for practical 
purposes, but which will be a somewhat too large deduction to make 
in estimating the productive part of the ration. 



48 



MAINTENANCE RATIONS OF FARM ANIMALS. 



SHEEP. 



Data regarding the maintenance rations of sheep are less com- 
plete than for those of cattle. No experiments are on record in 
which the requirement of available energy has been directly deter- 
mined, and but few respiration experiments have been made. Most 
of the recorded data are based upon live-weight experiments. 

In 1S67-GS Henneberg and liis associates 1 conducted a series of respiration 
experiments upon two mature sheep receiving approximately a maintenance 
ration of meadow hay. Two digestion experiments, including determinations of 
the nitrogen balance, were made with each of the animals. During each of 
these digestion experiments three respiration experiments were made upon the 
two animals together. The results of these determinations vary so little that 
their average is sufficient for our present purpose. Estimating, as in some of the 
experiments on cattle, that each kilogram of digestible organic matter contains 
approximately 3.5 therms of metabolizable energy, and further, that, as in the 
case of Kellner's steers, 43 per cent of the metabolizable energy of the feed 
could be stored up in the form of gain of flesh and fat, the following computa- 
tion per day and head may be made : 



Maintenance ration of sheep — Henneberg and Stohmann. 

Live weight, exclusive of wool kilograms 45. 4 

Digestible organic matter per day grams 539. 1 

Gain by animal : 

Protein do 7. 95 

Fat do 13. 75 

« 

Therms. 

Metabolizable energy of ration 0.5391X3.5 1.887 

Metabolizable energy equivalent to gain : 

Therm. 

Protein, 0.00795 kilo. X 5.7 0.0453 

Fat, 0.01375 kilo. X 9.5 . 1306 



. 1759 -K>. 43 . 409 



Metabolizable energy for maintenance 1. 478 

The foregoing ration is equivalent to 1.574 therms per 50 kilograms, or 
1.475 therms per 100 pounds, computed in proportion to the two-thirds power of 
the live weight. 

In 1872 Henneberg, Fleischer, and Miiller 2 began a series of respiration 
experiments upon sheep in which wheat gluten was added to a basal ration of 
hay and ground barley. The basal ration of the first period proved to be but 
slightly greater than the maintenance ration. Making the same calculations as 
before, but assuming that 50 per cent of the metabolizable energy of the ration 
might serve for the production of gain, since a portion of the ration consisted 
of grain, we have the following: 



1 Neue Beirrage, etc., pp. 68-286. 

2 Jahresbericht der Agriculturchemie, vol. 16-17, II, 145. 



MAINTENANCE RATIONS OF SHEEP. 



49 



Maintenance ration of sheep — Henneberg, Fleischer, and Muller. 

Live weight kilograms— 34. 20 

Digestible organic matter per day grams__ 562. 94 

Gain by animal : 

Protein grams__ 1.94 

Fat . grams__ 43.60 

Therms. 

Metabolizable energy of ration 0.56294X3.5 1.970 

Metabolizable energy equivalent to gain — 

Therm. 

Protein, 0.00194X5.7 0.01106 

Fat, 0.0436X9.5 .41420 

.42526-^-0. 50___ .851 

Metabolizable energy for maintenance 1. 119 

This result is equivalent to 1.441 therms per 50 kilograms or 1.350 therms per 
100 pounds live weight. 

Hagemann, 1 from the results of a digestion and metabolism experiment and of 
42 short 2 respiration periods with the Zuntz type of apparatus on a mature 
sheep averaging 50.33 kilograms live weight, computes an approximate energy 
balance which may be put in the following form, assuming that 50 per cent of 
the surplus metabolizable energy of the mixed ration might be recovered as 
gain: 

Maintenance ration of sheep — Hagemann. 





Income. 


Outgo. 


Feed: 

Alfalfa hay 


Therms. 
2.181 
1.524 


Therms. 


Corn meal 




Uneaten 


0.009 

1.332 
.146 

.914 
1.304 


Excreta: 

Feces 








Gain: Therm. 

1.44 grams protein 0.008 

46.20 grams fat 439 

. 447 h- 0. 50 










3.705 


3.705 



In addition to the foregoing experiments there are a number of digestion 
experiments by Wolff, in which the live weight of the animals was approxi- 
mately maintained. In 1871 3 two series of experiments were made upon 
the relative digestive power of three breeds of sheep for an approximate 
maintenance ration. A comparison of the live weights of the animals is possible 
only for the second series, in which the ration consisted of clover hay and 
potatoes. The total organic matter digested per day and head and the average 
live weights at the beginning and end of the experiment were as given in the 

J Archiv fur (Anatomie und) Physiologie, 1899, Snppl., p. 138. 

2 Usually not exceeding 30 to 40 minutes. 

3 Landwirtschaftliche Jahrbucher, vol. 1, p. 533. 

8489°— Bull. 143—12 4 



50 



MAINTENANCE EATIONS OF FARM ANIMALS. 



table, which also shows the metabolizable energy equivalent to the digested 
organic matter (3.5 therms per kilogram), both per head and per 50 kilograms 
live weight, computed in proportion to the two-thirds power of the latter. The 
average result is equivalent to 1.634 therms per 100 pounds live weight. 



Maintenance rations of sheep — Wolff. 



Breed. 


Number 
of 

animals. 


Live weight. 1 


Digested 
organic 
matter per 
day and 
head. 


Equivalent metaboliz- 
able energy per day. 


Initial. 


Final. 


Per head. 


Per 50 kilo- 
grams live 
weight. 


Electoral merino 


1 ; 

{ i 


Kilos. 
39. 85 
42. 05 
49. 85 
47. 45 
67. 55 
59. 05 


Kilos. 
39. 20 
40.50 
49.50 
47. 20 
66. 20 
59. 70 


Grams. 
345.35 
342.34 
537. 97 
523. 24 
680. 43 
620. 38 


Therms. 
1.209 
1.198 
1.883 
1.831 
2.382 
2. 171 


Therms. 
1.414 
1.361 
1.891 
1. 898 
1.963 
1.936 


Natives 


Southdowns 


Average 










1.779 


1.744 













1 Average of 5 or 6 consecutive days. 



In 1892-93 Wolff 1 made a series of experiments with sheep on the influence 
of salt upon digestibility. In the first two periods of this series an approxi- 
mate maintenance ration of 1,000 grams of meadow hay per day and head 
was fed. Since the salt was found not to affect the digestibility of the feed, 
we may use the results of the two periods as a basis for computing the main- 
tenance ration. The average live weights per head were as follows : 





January 
2, 3, and 4. 


February 
5, 6, and 7. 


Sheep No. 1 


42.9 
43.8 
42.8 
42.2 


44.0 
42.8 
44.5 
42.0 


Sheep No. 2 


Sheep No. 3 


Sheep No. 4 


Average 


42.9 


43.3 





The feed consumption was uniform with all the animals and the percentage 
digestibility showed but very slight variations, so that we may regard the 
average of the eight trials as representing approximately the maintenance 
ration. The average amount of organic matter digested per day and head 
was 476.28 grams. Reckoning, as before, 3.5 therms of metabolizable energy 
per kilogram, this corresponds to 1.667 therms per head, equivalent to 1.841 
therms per 50 kilograms or 1.725 therms per 100 pounds live weight, computed 
in proportion to the two-thirds power of the latter. 

Wolff 2 has also computed the digestible matter in the rations consumed by 
sheep in a number of the earlier experiments by Henneberg. The average of 
six rations which appeared amply sufficient for maintaining the live weight of 
the animal was, per head : 

Kilograms. 

Live weight 40. 05 

Organic matter digested . 566 

Equivalent metabolizable energy therms__ 1. 981 



1 Landwirtschaftliche Jabrbiicher, vol. 25, p. 175. 

2 Ernahrung der Landwirtschaftliche Nutztiere, pp. 416-419. 



MAINTENANCE RATIONS OF SWINE. 



51 



Computed in the usual way, this is equivalent to 2.300 therms per 50 kilo- 
grams. This is a much higher result than was obtained in any of the other 
experiments, and in view of the fact that the digestibility of the rations was 
estimated and that the feed was of a somewhat varied character it seems per- 
missible to omit this result from consideration. 

The results of the experiments cited, omitting the ones last men- 
tioned, may be summarized as follows: 

Daily maintenance rations of sheep. 



Kind of experiment, and investigator. 



Metabolizable energy, 



Per 50 kilo- 
grams live 
weight. 



Per 100 
pounds live 
weight. 



Respiration experiments: 

Henneberg and Stohmann 

Henneberg, Fleischer, and Miiller 
Hagemann 

Average 

Digestion experiments: 

Wolff, 1871 , 6 experiments 

Wolff, 1892-3, 8 experiments 

Average 

Average of all 



Therms. 
1. 574 
1.441 
1.304 



Therms. 
1. 475 
1.358 

1.222 



1.440 



1. 352 



1. 744 i 
1.841 j 



1.634 
1. 725 



1.793 



1.680 



1. 483 



It is of some interest to compare this average maintenance 
ration of sheep with the corresponding results for cattle. If we 
assume that the surfaces exposed by these two species are roughly 
proportional to the two-thirds powers of their live weights, the cor- 
responding maintenance ration for a 1,000-pound steer would 

be 1.483 8 = 6.885 therms of metabolizable energy as com- 

pared with an average of 10.50 therms for cattle. While such a 
comparison is, of course, but a rough approximation, it nevertheless 
seems to show conclusively that the metabolism of the sheep per 
unit of surface is distinctly lower than that of cattle. No obvious 
reason for such a difference suggests itself. That it can hardly be 
due to the direct effect of the wool in diminishing the radiation of 
heat will appear from a discussion, in a later section, of the influence 
of external temperature on the maintenance requirement. 

SWINE. 

Two determinations of the fasting katabolism of swine have been 
reported by Meissl, Strohmer, and Lorenz. 1 The experiments were 
made with the respiration apparatus, no calorimetric determinations 
being carried out. 

Computing the energy katabolized by the use of Rubner's factors for the en- 
ergy corresponding to the nitrogen and carbon excreted, the writer 2 obtained 



1 Zeitschrift fur Biologie, vol. 22, p. 63. 
- Principles of Animal Nutrition, p. 452. 



52 



MAINTENANCE RATIONS OF FARM ANIMALS. 



the figures contained in the third column of the following table. Kellner 1 has 
recomputed the results, using the exact figures for the carbon, nitrogen, and 
energy content of the flesh of swine which were obtained by Kohler, with the 
results shown in the last column. 



Fasting Jcatabolism of swine — Meissl, Strohmer, and Lorenz. 



Live 
weight. 



Fasting katabolism. 



Armsby. Kellner. 



Kilos. 
140 
120 



Therms. 
2. 607 
2. 291 



Experiment V.. 
Experiment VI. 



Computing Kellner' s figures to uniform live weight in proportion to the 
surface we have : 





Per 50 
kilo- 
grams. 


Per 100 
pounds. 


Experiment V 


Therms. 
1.377 
1.333 


Therms. 
1.290 

1.249, 


Experiment VI 


Average 


1.355 


1.270 





These figures, according to the principles enunciated in the foregoing pages, 
may be regarded as representing the available energy required for mainte- 
nance. No other direct determinations of this requirement appear to have been 
made. 

In addition to the foregoing, a number of live-weight experiments 
have been reported. 

Dietrich 2 determined the amount of feed required by growing pigs to maintain 
their live weight at different stages of growth. The trials were made when the 
animals reached approximately the weights of 50, 100, 150, and 200 pounds, 4 
animals being used. The digestibility of the ration fed at the weight of 150 
pounds was also determined. The actual average amounts of feed required per 
day and head were as follows : 

Maintenance rations of swine at different ages — Dietrich. 



Period. 


Averago 

live 
weight. 


Feed required for mainte- 
nance. 


Corn Mid- 
meal, dlings. 


Skim 
milk. 


I 


Pounds. 
49.62 
98. 75 
151. 25 
201.37 


Pounds. 1 Pounds. 
0.15 0.15 
.40 .40 
.80 .80 
.67 1.33 


Pounds. 
1.2 
1.6 
1.6 


II 


Ill 


IV 







1 Die Erniihrung dor Landwirtschaftliche Nutztiere, 5th ed., p. 156. 

2 Wisconsin Experiment Station, 16th Report, 1809, p. 31. 



MAINTENANCE KATIONS OF SWINE. 53 

Assuming the composition of the feeding stuffs used to be fairly represented 
by the averages given in Farmers' Bulletin 22 (revised) and using Jordan's 
digestion coefficients for middlings, oil meal, and skim milk, and Kellner's 
coefficients for corn meal, the writer has computed the digestible nutrients 
contained in the rations consumed with the results shown in the following table. 
The metabolizable energy of the rations has been computed from the amount of 
digestible nutrients, using the factors — 

Calories per gram. 



Digestible protein 4. 1 

Digestible nitrogen-free extract 4. 2 

Digestible crude fiber 3. 5 

Digestible ether extract 8. 8 



Computed digestible nutrients and metabolizable energy per day — Dietrich's 

experiments. 



Digestible nutrients per head. 

i 


Metabolizable energy. 


Period. 

j Protein. 

I 

1 


Carbohy- 
drates. 


Fat. 


Per head. 


Per 50 kilo- 
grams live 
weight. 


Per 100 
pounds live 
weight. 


1 Pounds. 

I ! 0.065 

II 1 .126 

III .204 

IV .205 


Pounds. 

0. 241 
.561 

1. 038 
L 159 


Pounds. 
0. 012 
.028 
.050 
.057 


Therms. 

0. 628 

1. 415 

2. 556 
2.817 


Therms. 
1. 069 
1. 523 
2. 069 
1.885 


Therms. 
1.002 
1.427 
1. 939 
1.766 



Taylor 1 reports quite similar experiments with animals weighing respec- 
tively 50, 100, and 150 pounds. Computed in the same manner as the previous 
experiments, the results are as follows : 



Maintenance rations of sicine at different ages — Taylor. 



Period. 


Average 

live 
weight. 


Feed required for mainte- 
nance. 


Shorts. 


Corn 
meal. 


Oil 
meal. 


I 


Pounds. 
52.1 
103.5 
157.0 


Pounds. 
0.48 
1.14 
1.20 


Pounds. 
0. 24 
.57 
.60 


Pounds. 
0.08 
.19 
.20 


Ill 


V 





Computed digestible nutrients and metabolizable energy per day — Taylor's ex- 
periments. 



Periods. 


Digestible nutrients per head. 


Metabolizable energy. 


Protein. 


Carbohy- 
drates. 


Fat. 


Per head. 


Per 50 kilo- 
grams live 
, weight. 


Per 100 
pounds live 
weight. 




Pounds. 


Pounds. 


Pounds. 


Therms. 


Therms. 


Therms. 


I 


0. 096 


0.434 


0. 025 


1. 105 


1. 821 


1.707 


Ill 


.288 


' 1. 030 


.058 


2. 618 


2.730 


2. 558 


V 


.240 


1.083 


.061 


2.753 


2. 174 


2.037 





1 Wisconsin Experiment Station Report, 1901, p. 67. 



54 MAINTENANCE EATIONS OE EARM ANIMALS. 



Carlyle 1 reports the average daily food for maintenance of 12 brood sows for 
eight weeks after weaning their pigs as follows : 

Pounds. 

Average live weight 306 

Feed per day and head : 

Corn 1.49 

Shorts i. 49 

Oil meal . 50 

Skim milk 6. 90 

The computed digestible nutrients and energy of the above ration are : 

Pounds. 

Digestible protein 0. 654 

Digestible carbohydrates 2. 307 

Digestible fat .117 

Equivalent metabolizable energy : Therms. 

Per head 6.079 

Per 50 kilograms live weight 3. 077 

Per 100 pounds live weight 2. 884 

In a preliminary report of experiments upon pig feeding, Dietrich 2 estimates 
the maintenance ration of growing pigs per 100 pounds live weight to be : 

Pounds. 

Digestible crude protein 0. 10 

Digestible carbohydrates . 40 

Digestible fat .04 

This ration, using the same factors as before for the metabolizable energy, 
is equivalent to 1.181 therms per 50 kilograms or 1.107 therms per 100 pounds 
live weight. 

The foregoing results show a wide range in the apparent food 
requirement for the maintenance of live weight. In general, the 
lower results seemed to have been reached with the younger animals. 
This may be due, however, to the fact that, as will be shown in a 
subsequent paragraph, the maintenance of live weight in a young 
animal is not necessarily synonymous with the maintenance of its 
store of potential energy. If we omit the results obtained with the 
50-pound animals and also omit Dietrich's results at the Illinois 
Station, since his experiments seem to have been with comparatively 
young animals, we find the range of results to be as follows: 





Per 50 
kilo- 
grams. 


Per 100 
pounds. 


Minimum 


Therms. 
1.523 
3. 077 
2. 243 


Therms. 
1.427 
2.884 
2. 102 


Maximum 







On the basis of respiration experiments by Meissl as discussed 
by Kellner, 3 four rations consisting of not dissimilar feeds showed 



1 Wisconsin Experiment Station. Bulletin 104, p. 31. 

2 Illinois Experiment Station, Circular 126, p. 116. 

3 Die Ernlihrung der Landwirtschaftliche Nutztiere, 5th ed., p. 157. 



MAINTENANCE RATIONS OF HORSES. 



55 



an approximate average utilization of 74.5 per cent of the meta- 
bolizable energy supplied in excess of the fasting katabolism. If 
we may apply this percentage to the average of the foregoing results 
regarding maintenance, we may compute the average requirement 
of available energy to be 2.243X0.745=1.671 therms per 50 kilo- 
grams, or 1.566 therms per 100 pounds, a result not differing very 
widely from the figures computed on a previous page from the results 
of experiments on the fasting katabolism, but with a very wide 
range of variation in individual cases. 

THE HORSE. 

The maintenance ration of the horse has been the subject of inves- 
tigation by Zuntz and Hagemann, Wolff, Miintz, and Grandeau and 
Le Clerc. 

ZUN1Z AND HAGEM ANN'S INVESTIGATIONS. 

Upon the basis of the results regarding the availability of energy 
for the horse, which have been described on pages 22-25, Zuntz and 
Hagemann 1 compute the fasting katabolism of the horse by sub- 
stantially the same method as that employed on pages 34-35 for cattle. 

For this purpose, they use those rest experiuieuts ou horse III iu which 
the feed consisted of oats, hay, and straw. From the results of the respira- 
tion experiments made within the first five hours after feeding, they compute 
the total energy katabolism per day in the manner indicated on page 22, and 
from this subtract the energy expended in the digestion of the feed (not 
including the work of mastication), computed as shown on page 23. The 
remainder, of course, is the katabolism due to internal work, together with any 
katabolism resulting from a possible demand for heat to maintain the body 
temperature. Their results may be tabulated as follows : 



Computed fasting katabolism of horse per dan and head — Zuntz and Hage- 
mann' s experiments. 





Live 
weight. 


Energy 
katabo- 
lism. 


Oats. 


Feed. 
Straw. 


Hay. 


Work of 
digestion. 


Fasting 
katabo- 
lism. 


Fasting 
katabo- 
lism per 
square 
centime- 
ter body 
surface. 


Season. 


















Gram- 






Kilos. 


Therms. 


Kilos. 


Kilos. 


Kilos. 


Therms. 


Therms. 


calories. 




Period a 


428.1 


12. 541 


6 


1 


7 


8.403 


4. 138 


80.7 


Winter. 


Period b 


434.1 


11.674 


6 


1 


6 


7. 704 


3. 970 


76.7 


Summer. 


Period e 


450.4 


12. 364 


6 


1 


6 


7. 704 


4. 660 


87.9 


Winter. 


Period/ 


449.1 


11. 783 


6 


1 


4. 75 


6. 830 


4. 953 


93.6 


Summer. 


Period i 


440.1 


11. 893 


6 


1 


6 


7. 704 


4. 189 


80.2 


Winter. 


Period n 


448.2 


11. 407 


£ 8 




5.1 


5.672 


5. 735 


108.5 


Summer. 


Period c 


442.2 


12. 450 





s 


10.5 


7. 340 


5.110 


97.6 


Do. 


Period No. 118c 


434.6 


11.021 


4.8 


0.8 


1.88 


4. 122 


6. 899 


133. 3 


Winter. 



In the experiments with a standard ration of 6 kilograms of oats, 
1 of straw, and 6 (or 7) of hay, the average computed fasting katab- 
olism for the three winter periods is 4.329 therms, while in the 



1 Loc. cit., pp. 283-284 and 425-426. 



56 



MAINTENANCE RATIONS OF FARM ANIMALS. 



single summer period it reaches the minimum of 3.970 therms. Zuntz 
and Hagemann consider that the latter represents approximately 
the minimum requirement for internal work and regard the higher 
figures obtained in the winter experiments as indicating a stimula- 
tion of the heat production by the low temperature to which the 
animal was exposed. The notably higher results obtained with the 
lighter rations they ascribe to a similar cause, viz, that the heat 
arising from the work of digestion and from the necessary internal 
work (fasting katabolism) was insufficient to maintain the body 
temperature. Accordingly, they regard the differences shown in col- 
umn 8 of the foregoing table as including in these cases not only the 
minimum necessary for internal work but also an expenditure for 
heat production. In other words, they consider that the critical tem- 
perature ( compare p. 71 ) for the horse is high as compared with that 
for cattle, and the critical amount of food small (compare p. 73). 
Earlier experiments 1 upon another horse in which lighter rations 
were fed confirmed this conclusion. 

On the average of the 8 most satisfactory experiments out of 12, the esti- 
mated total katabolism per day and head was 11.027 therms upon a ration 
consisting of 3.5 kilograms of oats, 0.5 of straw, and 2.5 of hay. Computed in 
the same manner as in the foregoing examples, the expenditure of energy in 
the digestion of this ration is equal to 3.782 therms, which leaves a remainder 
of 7.244 therms, equivalent to 140.3 gram-calories per square centimeter of sur- 
face. This is a higher figure than any of those contained in the foregoing table, 
although the total katabolism was not notably different. The authors conclude, 
therefore, that the small amount of heat liberated by the digestive work was 
compensated for by an increased katabolism of body tissue. 

From a balance experiment on the same animal in the respiration apparatus 
cf the Gottingen Experiment Station they also compute 2 the metabolizable 
energy required for maintenance by subtracting from the total nutrients di- 
gested the fat equivalent of the protein and fat gained by the animal. They 
thus reach a maintenance ration per 500 kilograms, live weight, of 3.265 
grams digestible nutrients, equivalent to 12.93 therms. Their final conclusion 
(loc. cit, p. 420) is that their animal required per head at least 11 therms, or per 
500 kilograms live weight 12.10 therms, of heat to maintain his body tempera- 
ture. In other words, this is the minimum of metabolizable energy which must 
be supplied in a maintenance ration, since if less be present, even although the 
ration supplies the requisite amount of available energy, body tissue will still 
be katabolized for the production of the heat necessary to maintain the body 
temperature. 

Computed to 1,000 pounds live weight in proportion to the two- 
thirds power of the latter, Zuntz and Hagemann's maintenance 
ration is : 



1 Landvvirtschaftliche Jahrbiicher, vol. 18, p. 1 ; vol. 27, Erganzungs Band III, pp. 
356-257. 

2 Ibid., p. 423-424. 



Available energy for internal work 

Additional required for heat production 



Therms. 
_ 4.08 
_ 7. 80 



Total metabolizable energy required. 



11. 88 



MAINTENANCE RATIONS OF HORSES. 



57 



The maintenance requirement as measured by the computed fast- 
ing katabolism is notably less than that of cattle. The same criti- 
cisms which have been made of Zuntz and Hagemann's conclusions 
as regards availability are also applicable, of course, to his compu- 
tation of the maintenance requirement. 

WOLFF'S INVESTIGATIONS. 

Wolff has also determined by a different method the maintenance 
ration of the horse in the experiments whose results as regards 
the available energy of feeds have already been mentioned on page 
25. As there noted, the amount of work performed by the horse 
was adjusted so as to be as nearly as possible in equilibrium with 
the feed consumed. Wolff's experiments were made with a sweep 
power arranged to serve also as a dynamometer. The actual meas- 
urements of the work performed, except in the later experiments, 
proved to be too low ; but Wolff believes them to be relatively correct, 
so that the ratio between the work as measured and the additional 
feed required to produce it may still serve as the basis of computation. 

In the experiments of 1877-1886 1 it was found that the work performed in 
100 revolutions of the dynamometer required the addition to the ration of 
315 grams of digestible nutrients. It is important to note, however, in view 
of what follows, that this additional digestible material included no digestible 
crude fiber — that is, that it was practically derived from the grain added in 
the periods of heavier work. Subtracting from the total digestible nutrients 
of the ration, therefore, an amount computed on this basis to be equivalent to 
the work done leaves-a remainder representing the nutrients required for mainte- 
nance on the virtual assumption that all the work done was performed at the 
expense of nutrients derived from the grain. The results of these computa- 
tions are summarized in the following table : 



Maintenance rations of horses — Wolff, 1877-1886. 



Animal. 


Number 
of experi- 
ments. 


Total 
nutri- 
ents. 


Nutri- 
tive 
ratio. 


Live 
weight. 


Number 
of revolu- 
tions. 


Equiva- 
lent nutri- 
ents. 


Mainte- 
nance 
ration 
by differ- 
ence. 


Horse II: 

1881- 82 

1882- 83 

1883- 84 

Horse III: 

1881- 82 

1882- 83 

1883- 84 

1885 

Average 


4 


Grams. 
6, 305. 6 


1:5. 79 


Kilos. 
521 


600 


Grams. 
1,890 


Grams. 
4, 416 


7 
4 

6 


5,831.1 
6, 748. 3 
5, 920. 2 


1:6. 64 
1:6.37 
1:7.26 


477 

486 
457 


546 
662 
567 


1,720 
2,085 
1,786 


4,111 

4,663 
4, 134 


17 


6,078.4 


1:6. 80 


473 


577 


1,818 


4,260 


6 
6 
5 
4 


5,313.8 
6,061.3 
5,734.8 
5,761.2 


1:7. 16 
1:6. 88 
1:7. 55 
1:7. 57 


454 
469 
473 
473 


404 

683 
580 
575 


1,273 
2,152 
1,827 
1,811 


4,041 
3,909 
3.908 
3,050 


21 


5,717.8 


1:7. 29 


467 


501 


1,766 


3,952 



1 Grundlagen fur die rationelle Fiitterung des Pferdes, 1886, 66-155 ; Neue Beitrage ; 
Landwirtschaftliche Jahrbiicher, vol. 16, Erganzungs Band III, 1-48. 



58 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Computed to 500 kilograms live weight on the basis of what Wolff regards 
as the normal weights of the animals, the foregoing maintenance rations are: 

Grams. 

Horse I 4, 143 

Horse II 4,260 

Horse III 4,167 

A series of similar experiments on horse III, weighing 475 kilograms, in 1885- 
86, 1 computed in substantially the same way, gave results for the maintenance 
ration agreeing well with those of earlier years, viz : 



Maintenance rations of a horse — Wolff, 1885-86. 



Period. 


Per head. 


Per 500 
kilo- 
grams. 


I 


Grams. 
3,934 
3.984 
4,001 
4,094 
4,094 


Grams. 
4,141 
4, 194 
4,212 
4,310 
4,310 


II 


Ill and V 


Vllb 


VIII 


Average 


4,021 


4,232 





In a succeeding period (IX), however, in which hay alone was fed, a de- 
cidedly higher result was obtained, viz, 4,357 grams per head, or 4,586 grams 
per 500 kilograms. 

In these earlier experiments, in accordance with the views then prevalent, 
Wolff regarded the so-called nutrients as of equal value whatever their source. 
The experiment with hay, just mentioned, however, suggested that such was not 
the case and this suspicion was confirmed by later investigations which clearly 
showed the superiority of the digestible matter of grain over that of hay. 
This superiority was not apparent in the earlier experiments because the pro- 
portions of grain and coarse fodder were not widely different in the several 
experiments, the coarse fodder furnishing on the average fully one-half of 
the dry matter fed. 

This difference, suggested by the experiment on hay, was demonstrated by a 
comparison by Wolff 2 of his own results with those obtained by Grandeau and 
Le Clerc 3 in experiments upon two cab horses receiving only a small amount of 
walking exercise. The ration used by the latter experimenters consisted of 
about 75 per cent of grain as against less than 50 per cent in Wolff's experiments, 
and from it Wolff computes an average maintenance ration per 500 kilograms 
of 3,626 grams of digestible nutrients as compared with the 4,000 to 4,200 grams 
of the foregoing table. 

Direct experiments by Wolff 4 likewise show that the digestible nutrients of 
concentrated feed (oats) are more valuable for work production than those of 
coarse feed (hay). The experiments were made in the manner already de- 
scribed, the draft being uniformly 60 kilograms. Although the measurements 
of the work actually done are probably incorrect, it may be assumed to have 
been substantially proportional to the number of revolutions of the dyna- 
mometer. A ration of 3 kilograms of hay and 5.5 kilograms of oats served as 
the basal ration, to which was added on the one hand 4 kilograms of hay and 

1 Landwirtschaftliche Jnhrbueher, vol. 13, Ergiinzungs Band III, p. 32. 

2 Ibid., pp. 73-81. 

3 L' Alimentation du Cheval de Trait, 1883, II, 86 and 131. 
*Loc. cit., pp. 84-95. 



MAINTENANCE RATIONS OF HORSES. 



59 



on the other 1| kilograms of oats. The nutrients digested in each case and 
the equivalent amounts of work secured were : 



Nutrients equivalent to work — Wolff, 1886-87. 



Period. 


Ration. 


Digested. 


Equivalent 
work. 


Protein. 


Crude 
fiber. 


Nitrogen- Ether 
free extract, extract. 


Total (fat 
X 2.4). 


I-III... 

V 

VI 
V 


7 kilograms hay, 5.5 kilo- 

3 kilograms hay, 5.5 kilo- 
grams oats 

4 kilograms hay 

Per 100 revolutions 


Grams. 
822. 58 

626.46 


Grams. 
816.68 

422. 74 


Grams. 
3,889. 64 

3,068. 78 


Grams. 
186. 72 

184. 78 


Grams. 
5, 973. 62 

4, 561. 13 


Revolutions. 

750 

350 


196. 12 


393. 94 


821. 18 


1.94 


1,412.49 
353. 12 


400 


3 kilograms hay, 7 kilo- 
grams oats 

3 kilograms hay, 5.5 kilo- 
grams oats 

].5 kilograms oats 

Per 100 revolutions 












754.52 
626. 46 


355. 24 
393. 94 


3, 719. 24 
3,068. 46 


252. 17 
184. 78 


5, 434. 21 
4, 561. 13 


700 
350 


128. 06 


-67. 50" 


650. 78 


67.39 


873. 08 
249. 45 


350 















The relative value of the digested matter of hay and of oats for work 
production in these trials was thus approximately as 5 : 7. 

The digestible nutrients added to the ration by the oats in period VI in- 
cluded no crude fiber, and, as the table shows. 249 grains of these fiber-free 
nutrients were found equivalent to 100 revolutions of the dynamometer with 
a draft of 60 kilograms, which is practically equivalent to the 315 grams per 
100 revolutions with 76 kilograms draft found in the earlier experiments 
(p. 57) in which also, as was noted, the additional nutrients were practically 
fiber-free. Of the digestible nutrients added to the ration in the form of hay 
in period I-III, on the other hand, over one- fourth consisted of crude fiber, 
and in this case 353 grams were found to be equivalent to 100 revolutions 
of the dynamometer. If, however, the digestible crude fiber be omitted in this 
case, it appears that the fiber-free nutrients of the hay were practically equiv- 
alent to those of the oats, 255 grams being required for each 100 revolutions. 

As noted previously, Wolff recomputed his experiments on the assumption 
that the crude fiber was valueless, and obtained results expressed in terms of 
fiber-free nutrients which were consistent among themselves and agreed with 
those obtained by Grandeau. The following table contains a summary of the 
results obtained for the maintenance ration expressed both in terms of total 
nutrients (including digestible crude fiber) and of fiber-free nutrients: 

Nutrients for maintenance per 500 kilograms live weight — Wolff. 



Experiments. 



Including 
fiber. 



Fiber-free. 



Experiments of 1881-1885; 

Horse I t_- 

Horse II 

Horse III 

Average 

Experiments of 1885-86— Horse III: 

Period I 

Period II 

Period III and V 

Period VII 

Period VIII 

Period IX 

Average 

1 Omitting period IX 



Grams. 


Grams. 


4,143 


3,378 


4,260 


3,282 


4,167 


3,306 


4, 190 


3.322 


4,141 


3,142 


4, 194 


3,353 


4,212 


3,413 


4,310 


3,549 


4,310 


3,490 


[4, 586] 


3,335 


i 4,232 


3,430 



60 MAINTENANCE RATIONS OF FARM ANIMALS. 



Nutrients for maintenance per 500 kilograms live weight — Wolff — Continued. 



Experiments. 


Including 
fiber. 


Fiber-free. 


Grandeau's experiments: 

Horse II 


Grams. 
3,636 
3,617 


Grams. 
3,324 
3,328 


Horse III 




3,626 


3,326 


Experiments of 1886-87: 

Period I-III 


1,202 
4,150 
3,792 
3,738 


3,342 
3,429 
3,329 
3,364 


Period IV 


Period V 


Period VI 


Average 


3.971 


3,366 





The figures inclusive of the crude fiber, as computed by Wolff, evi- 
dently correspond approximately with the amounts of metabolizable 
energy contained in various mixed rations which were sufficient for 
maintenance. In the earlier experiments, and in those later ones in 
which approximately equal proportions of hay and grain were con- 
sumed, the amount is approximately 4,200 grams per 500 kilograms 
live weight, which, using Zuntz and Hagemann's factor of 3.96 
calcries per gram, is equal to 16,632 calories. In the later experi- 
ments, in which a larger proportion of grain was fed, the total 
nutrients required for maintenance ranged from 3,600 to 3,700 grams, 
equivalent to from 14,257 to 14,652 calories. In other words, the 
amount cf metabolizable energy necessary for maintenance varied 
with the proportion of coarse fodder present, as would be expected 
from the results with cattle recorded on previous pages. 

The maintenance ration in terms of metabolizable energy, as 
thus computed, is comparable with that estimated by Zuntz and 
Hagemann, in the manner explained on pages 55-56, from the total 
heat production of the animal. That Wolff's results are higher is 
probably due to the relatively larger proportion of crude fiber in his 
maintenance rations, since, as shown on page 57, the work is assumed 
by Wolff's method of calculation to have been done at the expense of 
the nutrients of the grain, and consequently the remaining portion of 
the ration, which is regarded as the maintenance portion, was rela- 
tively poorer in grain and richer in coarse fodder. 

Zuntz and Hagemann 1 attempt to estimate the difference due to 
the latter fact. They average 31 of Wolff's experiments, divided 
into two groups, viz, those on light and on heavy work, correcting 
the actual amount of work done for the loss of live weight and 
likewise for what they regard as Wolff's error in his estimate of the 
energy expended in locomotion. They also correct Wolff's estimate 



1 Loc. cit., pp. 4liO-424 ; Principles of Animal Nutrition, p. 546. 



MAINTENANCE RATIONS OF HOESES. 



61 



of the energy of the digested matter by the use of the factor 3.96 
calories per gram instead of 4.1 calories per gram. Their compari- 
son of the two groups gives them by difference 31 per cent as the 
proportion of the available energy of the digested nutrients which 
was recovered in the form of work, a percentage corresponding very 
closely to that found for the work of draft in their experiments, 
viz, 31.4. Upon this basis, they compute in each group the amount 
of nutrients required for the total work done and by subtraction 
the total digestible nutrients required for maintenance. 

Their results for an animal weighing approximately 500 kilograms 
are as follows, the equivalent metabolizable energy being obtained 
by the use of Zuntz and Hagemann's factor of 3.96 calories per gram. 
The average does not differ materially from that computed directly 
from Wolff's later experiments. 



Total 
digestible 
nutrients. 



Equivalent 
metaboliz- 
able energy. 



Periods of light work. . 
Periods of heavy work 

Average 



Grams. 
3,776 
3,763 



Therms. 
14.95 
14.90 



3,770 



This result they compare with that obtained by them in a balance 
experiment with a respiration apparatus from which, as noted on 
page 56, they compute a maintenance ration of 12.93 therms. 
Their ration, however, contained notably less crude fiber than did 
Wolff's rations, the differences being as shown in the following 
table, which includes also the equivalent digestive work, estimated 
by Zuntz and Hagemann at 2.65 calories per gram : 





Difference 
in crude 
fiber fed. 


Equivalent 
digestive 
work. 


Periods of light work 


Grams. 
974 
956 


Therms. 
2.58 
2.53 


Periods of heavy work 


Average 


965 


2.56 





Subtracting this amount from the average computed from Wolff's 
experiments leaves a remainder of 12.37 therms as the metabolizable 
energy which would have been necessary for maintenance had Wolff's 
rations contained no more crude fiber than Zuntz and Hagemann's. 

Wolff's experiments afford no data for computing in terms of 
available energy the maintenance requirement in the sense in which 
this term is used by Zuntz and Hagemann and in the discussion of 
the maintenance requirements of cattle, on pages 33 to 35, viz, as 



62 MAINTENANCE RATIONS OF FARM ANIMALS. 

equivalent to the necessary demand for internal work. Even if we 
follow Wolff in regarding the energy of the fiber-free nutrients as 
an approximate expression of the available energy, his computation 
of the fiber-free nutrients required for maintenance simply shows the 
amount of available energy (in this sense) present in a maintenance 
ration, but gives no indication of how much of this may have been 
consumed in simple heat production. 

MUNTZ'S EXPERIMENTS. 

Miintz, 1 in 1878-79, attempted to determine the maintenance ration 
of the horse by a different method, viz, by starting with an insufficient 
ration and gradually increasing it until an equilibrium between food 
and live weight was secured. His experiments were made upon 
horses of the Paris Omnibus Co. whose work ration was known from 
previous experiments. Upon one-third of their regular working 
ration four horses lost in from one to one and a half months an aver- 
age of 1.02 pounds per day and head. The ration was then increased 
to one-half of the work ration. Upon this nine horses, including the 
four used in the previous experiments, gained on the average 1.08 
pounds per day and head. Upon decreasing the ration to five- 
twelfths of the work ration, six other horses gained 0.46 pound per 
day and head. The amount of total organic matter consumed by 
the animals is recorded. Estimating from this the total digestible 
nutrients and computing the metabolizable energy of the latter at 
the rate of 3.96 calories per gram, the last two rations afforded the 
following results : 

Metabolizable energy in rations of horses — Miintz. 





Average 
gain in 
weight 

per day. 


Average 

live 
weight. 


Digesti- 
ble nu- 
trients. 


Metabolizable en- 
ergy. 


Per head. 


Per 1,000 
pounds 

live 
weight. 


One half of work ration 


Kilos. 
+0.49 
+0.19 


Kilos. 
545 
523 


Grams. 
4,102 
3,417 


Therms. 
16. 24 
13.53 


Therms. 
14.37 
12. 31 


Five-twelfths of work ration 





GRANDEAU AXD LE CLERC'S RESULTS. 



Grandeau and Le Clerc, 2 in addition to the experiments recorded 
in connection with Wolff's results, fed five cab horses a daily ration 
of 8 kilograms of hay during a total of 14 periods of a month each 
(1 to 5 periods for each animal), during each of which the digesti- 
bility of the ration was determined. The animals had only a small 



1 Annales de l'lnstitut National Agronomique, Tome 3, 1878-79. 

2 L' Alimentation du Cheval de Trait, 1883, III. 



TRUE MAINTENANCE AND LIVE-WEIGHT MAINTENANCE. 



63 



amount of walking exercise daily. The following are the results of 
the several periods : 

Metabolizable energy in rations of horses — Grandcau and Le Clerc. 



Total 
digestible 
nutri- 
ents. 1 



Equiva- 
lent me- 
taboliza- 
ble en- 
ergy. 



Average 
daily 

gain or 
loss of 

weight. 



Average 

live 
weight. 



Horse 30845 (No. 1): 
January, 1884... 

April, 1884 

August, 1884 

September, 1884. 
October, 1884.... 



Grams. 
2,895.3 
2,351.9 
2,795.5 
2,927.8 
2,897.1 



Therms. 
11. 467 
9.315 
11.071 
11. 595 
11.473 



Kilos. 
-0. 19 
+0. 47 
+0. 03 

2 -0. 03 
2 0. 00 



Kilos. 
394.9 
379.2 
365.0 
366.3 
366.0 



Average. 



m. 5 



10. 9S3 



+0. 06 



374.3 



Horse 29475 (No. 2): 
November, 1883. 

Horse 29466 (No. 2): 

May, 1884 

June, 18S4 

July, 1884 



3,041.4 



12.045 



+0.59 



423.6 



2,470.2 
2,909.5 
2,692.8 



9.7S4 
11. 523 
10. 663 



+0.42 
+0.13 
+0.18 



404.0 
407.1 
410.6 



Average. 



2,690.8 



10. 656 



+0. 24 



407.2 



Horse 29407 (No. 3): 
December, 18S3. 

Horse 26925 (No. 3): 

March, 1884 

June, 1S84 

Julv, 1SS4 

August, 1884... 



3,062.1 



12. 128 



2,726.S 
2, 644. 5 
2,719.4 
2,S37.9 



10. 799 
10. 473 
10. 770 
11. 238 



+0. 82 
+0.27 
0.00 
-0.01 



413.! 



419.0 
3S4.3 
387.7 
388.4 



Average. 



2,732.2 



10. S20 



+0.: 



394. 



1 Including fat X2.4. 

2 Omitting last day of each month. 

On the average of all the periods, the results per day and head, 
were as follows : 

Total digestible nutrients ( fat X 2.4) grains— 2,783.7 

Equivalent metabolizable energy, at 3.96 calories per 

grain tnerins__ 11. 03 

Daily gain in weight kilograms__ 0. 19 

Average live weight do 393. 6 

The foregoing ration, which was apparently somewhat more than 
a maintenance ration, is equivalent to 12.12 therms of metabolizable 
energy per 1,000 pounds live weight. This is materially less than 
was obtained in "Wolff's experiments and about the same as that found 
by Zuntz and Hagemann for rations containing much grain. 



TRUE MAINTENANCE AND LIVE - WEIGHT MAINTENANCE. 

The maintenance of an animal in the strict scientific sense signifies 
the preservation of the store of matter and of potential energy con- 
tained in the body, and only a ration which effects this is really a 
maintenance ration. As has appeared in the foregoing pages, how- 
ever, much of our recorded information regarding the maintenance 



64 



MAINTENANCE RATIONS OF FARM ANIMALS. 



ration is derived from experiments in which the sufficiency of the 
ration was judged of from its effect in maintaining the live weight 
of the animal. In experiments on mature animals extending over a 
considerable period of time, it is unlikely that any gross error is 
involved, especially if determinations of the nitrogen balance show 
the protein supply to be adequate. In short periods, on the other 
hand, and especially in experiments upon young animals, the live 
weight is a notoriously untrustworthy guide. The general reasons 
for this are familiar, but in young animals another very important 
factor enters into consideration. As is well known, the tendency to 
growth is one of the most marked characteristics of young animals. 
Waters 1 has shown that this impulse to increase of tissue is so marked 
that it may apparently take precedence over the demand for main- 
tenance, so that an animal may continue to increase in size of skeleton 
for a considerable time even on a submaintenance ration. 

Some 15 immature cattle were fed for considerable periods on ra- 
tions just sufficient to maintain their live weight. Under these condi- 
tions the animals continued to grow in height, in depth of chest, and 
length of head. At the same time, however, there was an evident 
falling off in the amount of fat tissue, both as judged by the eye and 
as shown by the appearance and by the chemical composition of the 
carcass. Histological studies, too, showed a reduction in the size of 
the fat cells, and analysis of the adipose tissue showed a lower fat and 
higher water and protein content than in check animals. What 
occurred was evidently a consumption of body fat to supply energy, 
while at the same time an approximately equal weight of protein tis- 
sue was produced which, on account of the relatively low energy value 
of protein and of the relatively large amount of water accompanying 
it, represented a much smaller quantity of energy than did the fat tis- 
sue which disappeared. In other words, the rations were not really, 
but only apparently maintenance rations. It is perhaps hardly correct 
to say that in these experiments growth was maintained at the ex- 
pense of the fat of the tissues. A more exact statement of the case 
would be that the increase of protein tissue and water masked the 
loss of fat. Presumably this effect would be less marked in more 
mature animals, in which the true maintenance and live-weight 
maintenance would doubtless approach each other closely when meas- 
ured over long periods. 

FACTORS AFFECTING THE ENERGY REQUIREMENT. 

The results of the experiments upon farm animals reported on 
previous pages render it evident that the actual maintenance require- 
ment, even when computed to a uniform weight or size, is more or 

1 Society for the Promotion of Agricultural Science, Proceedings of 29th Annual Meet- 
ing, p.' 71. 



FACTORS AFFECTING THE ENERGY REQUIREMENT. 



65 



less variable. For example, in the case of cattle, for which the most 
extensive and accurate data are available, the range of the energy 
requirement per day and 1,000 pounds live weight for thin animals 
in those experiments which are apparently the most accurate is 4.9 
to 7.3 therms available energy or 8.5 to 12.8 therms metabolizable 
energy. Several causes may be responsible for these variations. 

MUSCULAR ACTIVITY. 

In considering the factors of the fasting katabolism (p. 9), atten- 
tion was called to the large share which the muscles, and especially 
the voluntary muscles, have in the heat production of the animal. 
Even in a state of the most complete rest possible, a very considerable 
share of the total katabolism takes place in these tissues, due, pre- 
sumably, to the state of constant slight tension or " tonus " of the 
living muscle. 

MINOK MUSCULAR MOTIONS. 

It is rarely the case, however, that an animal, even when at rest 
in the ordinary sense, does not execute more or less motions of various 
parts of the body, all of which involve an expenditure of energy, and 
even apparently insignificant movements may materially increase the 
amount of metabolism. 

Zuntz and Hagemann, 1 for example, report a respiration experi- 
ment upon a horse in Avhich the uneasiness caused by the presence of 
a few flies in the chamber of the apparatus caused an increase of 10 
per cent in the metabolism. Johansson 2 compared the excretion 
of carbon dioxid by a fasting man when simply lying in bed (awake) 
with that occurring when all the muscles were as perfectly relaxed 
as possible. The results per hour were : 

Excretion of C0 2 oy fasting man. 

Grams. 

Lying in bed 24 .94 

Complete muscular relaxation 20 .72 

Benedict and Carpenter 3 have compared the metabolism of men 
during sleep with that of the same subjects lying quietly in bed im- 
mediately after waking. In the three cases which they regard as 
strictly comparable the increase in the heat production during the 
waking period ranged from 5.8 to 15.2 per cent, averaging 11.4 
per cent. 

If, then, these comparatively insignificant movements have such a 
striking effect upon the metabolism, it is evident that the amount of 
muscular activity must be an important factor in determining the 

1 Landwirtschaftliche Jahrbiicher, vol. 23, p. 161. 

2 Skandinavisches Archiv fur Physiologic*, vol. 8, p. 85. 

3 Carnegie Institution of Washington, Publication 126, p. 241. 

8489°— Bull. 143—12 5 



66 



MAINTENANCE RATIONS OF FARM ANIMALS. 



relative maintenance requirements of two animals even though their 
minimum physiological requirements may be identical. In experi- 
ments of any considerable duration on normal animals, it is impossible 
to avoid more or less expenditure of energy in this incidental muscular 
work, while it is often a matter of difficulty to make the different 
periods of an experiment comparable in this respect. 

LYING AND STANDING. 

Furthermore, considerable muscular exertion is involved during the 
waking hours in maintaining the relative position of the different 
members of the body. This is notably true of the effort of standing. 
In experiments by Armsby and Fries 1 the heat radiated per 
minute by a steer while standing was found largely to exceed that 
given off while lying, the excess in 25 experiments ranging from 28.3 
to 64.5 per cent, although there were indications that the amount of 
feed consumed was also a factor. 

On the other hand Dahm, 2 working in Zuntz's laboratory and by 
his methods, found an increase of only 8 per cent in the respiratory 
excretion of C0 2 by a young bull when standing as compared with 
that when lying, but Zuntz 3 himself in earlier experiments on a dog 
observed differences similar to those found by Armsby and Fries for 
cattle, the average oxygen consumption per minute being while lying 
174.3 c. c. and while standing 245. G c. c, or an increase of 41 per cent. 
Benedict 4 observed an increase of from 13.3 to 18.8 per cent, or an 
average of 16.5 per cent, in the heat production of man when standing 
as compared with that observed when sitting quietly in a chair. 

It is clear, then, that of two animals, one of which lies down for 12 
hours and the other for 8 hours out of the 24, the former will, other 
things being equal, require less energy for maintenance. In the 
results regarding the maintenance ration thus far reported, with 
the exception of the Pennsylvania experiments, this factor has not 
been taken into account. 

INDIVIDUALITY. 

It appears quite probable that those differences between the main- 
tenance requirements of different animals which are ascribed some- 
what vaguely to " individuality " are due to a large extent to varying 
amounts of muscular activity. In general, the nervous, restless 
animal will have a higher maintenance requirement than the quiet, 
phlegmatic one. Thus the table on page 40 shows that Armsby and 

1 Bureau of Animal Industry, Bulletins 51, 74, 101, and 128. 

2 Biochemische Zeitschrift, vol. 28, p. 494. 

"Archly fur die gosammte Physiologie des Menschen und der Thiere (Pfliiger), vol. G8, 
p. 191. 

4 Loc. fit, p. 244. 



FACTORS AFFECTING THE ENERGY REQUIREMENT. 



67 



Fries's steer A had in every case a materially lower maintenance 
requirement than steer B, even when the results were corrected to an 
equal number of hours standing per day. Computed per 1,000 pounds 
live weight and corrected to 12 hours standing, the results for avail- 
able energy were as follows : 



Available energy required for maintenance — Armsby and Fries. 





Steer A. 


Steer B. 




Therms. 


Therms. 




6. 23 


7.06 
6. 38 


1906 


5.70 




4.86 


6.50 







Steer B was an animal of rather pronounced dairy type and of a 
nervous disposition, and in all probability his higher maintenance re- 
quirement is to be ascribed to this fact. There can be little doubt 
that temperament is an important factor in determining the main- 
tenance requirement and that there may be a considerable range of 
individual differences in this respect. 

Similarly, any conditions tending to affect the degree of muscular 
activity will also tend to affect the maintenance requirement. The 
steer confined in a stall, for example, is likely to take less muscular 
exercise and therefore to require a smaller amount for maintenance 
than one simply confined to a pen or an open yard. The animal 
comfortably bedded and thereby induced to spend much of his time 
in lying down will consume a smaller portion of his feed for mainte- 
nance than one kept under less comfortable conditions. Any sort of 
excitement is likely to cause increased muscular activity and corre- 
spondingly increased consumption of food for maintenance. 

CONDITION. 

The condition of an animal — that is, the amount of adipose tissue 
carried — seems to influence the maintenance ration, at least in 
the case of cattle. This point was first investigated by Kellner. 1 
His average result for three fat cattle, as shown in the table on 
page 43, is considerably higher when computed to the same live 
weight — that is, per unit of surface — than that for the seven lean 
animals, viz : 

Unfattened 10. 87 therms metabolizable energy per 1,000 pounds live weight. 

Fattened 15. 05 therms metabolizable energy per 1,000 pounds live weight. 

Only one animal, however, was common to the two groups, viz, 
steer B, the results on which were excluded from the average of the 
unfattened animals on the ground that it was abnormally high, since 
the animal never lay down during the experiments. Curiously 



1 Die Landwirtschlichen Versuchs-Statioioen, vol. 50, p. 245 ; vol. 53, p. 14. 



68 



MAINTENANCE RATIONS OF FARM ANIMALS. 



enough, this animal showed the lowest maintenance ration of the 
three fattened animals and, moreover, one which is distinctly less 
per unit of computed surface than in the unf attened state, viz : 

Uufattened 14. 72 therms metabolizable energy per 1,000 pounds live weight. 

Fattened 13. 86 therms metabolizable energy per 1,000 pounds live weight. 

No other respiration experiments upon the relative maintenance 
requirements of fattened and unf attened animals are on record. 
Evvard's live-weight results, however, as given in the table on page 
47, appear to confirm Kellner's conclusion that the relative mainte- 
nance ration of fattened animals is greater than that of the same 
animals unfattened. 

One obvious reason why the maintenance requirement should be 
greater in the former case is the presumably greater muscular effort 
expended in standing, due to the greater weight to be supported. 
Zuntz and Hagemann in experiments upon the horse carrying weight 
on its back found that this increase was proportional to the amount of 
weight added. The increase indicated by Kellner's averages, how- 
ever, is greater than would be computed on this assumption, and the 
same is true of Evvard's fat animals, the difference becoming greater 
as the animals become fatter. 

AGE. 

The energy requirement of a young animal is naturally smaller per 
head than that of an older animal on account of the difference in 
size. Whether there is any difference in the relative requirements — 
that is, in the requirement computed to uniform weight or surface — 
is not altogether clear, few specific results on farm animals being on 
record. Evvard's results on yearlings, page 46, are somewhat higher 
than most of the results which have been obtained with mature 
cattle, although, of course, these figures do not refer to the same 
individuals at different ages. Armsby and Fries, 1 in a series of respi- 
ration calorimeter experiments upon the same two animals in three 
successive years, observed a progressive decrease in the maintenance 
requirement of yearlings, 2-year-olds, and 3-year-olds when corrected 
to a uniform number of hours standing and computed to equal ex- 
ternal surface (that is, in proportion to the two-thirds power of the 
weight ) . 

Somewhat extensive data are on record regarding the metabolism 
of man at different ages. A summary and discussion of these by 
Tigerstedt 2 seem to show clearly that, leaving out of account infants 
and very aged persons, the metabolism per unit of surface diminishes 
from youth to maturity. In view of the slow development of man, 
these results are comparable to such as might be obtained during the 
first 6 to 12 months of the life of ordinary domestic animals and for 



1 Bureau of Animal Industry, Bulletin 128, p. 55. 

2 Nagel's Handbuch der Physiologie des Menschen, I, 469. 



EXTERNAL TEMPERATURE. 



69 



these ages we have few satisfactory determinations of the mainte- 
nance requirement. The results upon swine cited on previous pages 
seem, it is true, to indicate the contrary relation, viz, a lower relative 
maintenance requirement for young animals. These results, how- 
ever, are based upon live-weight experiments and, as already noted, 
are possibly lower than the true maintenance ration. 

If it be true that the maintenance rations of young animals are 
relatively greater than those of older ones, we may fairly presume it 
to be due to a considerable extent to the greater amount of muscular 
activity usually exhibited by young animals. 

EXTERNAL TEMPERATURE. 

Farm animals belong to that general class known as warm-blooded 
or homoiothermic animals, whose bodies maintain a nearly constant 
temperature during health, regardless of that of their surroundings 
unless the latter be extreme, in which case death soon results. 

REGULATION OF BODY TEMPERATURE. 

Obviously, the regulating mechanism which maintains a constant 
temperature in spite of variations in the heat production of the body 
and in the temperature of its surroundings must be very efficient 
and very exactly adjusted. The regulation is effected in general in 
two ways, which may be called, respectively, physical and chemical 
regulation. 

The heat of an animal escapes from the surface of tne body chiefly 
through the skin, but to some extent also through the air passages, 
being removed both by conduction, by radiation, and by the evapora- 
tion of water. A rise of external temperature tends to check the out- 
flow of heat exactly as it would in the case of an inanimate body. 
This tendency is compensated by a nervous reflex, which allows the 
capillary blood vessels of the skin to enlarge so that more blood flows 
through them, thus tending to raise the temperature of the surface 
and increase the outflow of heat. This phenomenon is readily ob- 
served in the flush which follows exposure to high temperatures. This 
method of regulation is analogous to opening the windows of a room 
to cool it. If the external temperature continues to rise, perspiration 
appears, or in the case of animals that have no sweat glands, like the 
dog, a peculiar form of breathing sets in, and relatively large amounts 
of water are evaporated from the skin or from the tongue and the in- 
terior of the mouth and throat. In this way large quantities of heat 
are carried off as the latent heat of evaporation of water, somewhat as 
an overheated room may be cooled by sprinkling the floor. When the 
external temperature falls again, the process is reversed. Sensible 
perspiration decreases and the blood is diverted from the capillaries 
of the skin to the internal capillaries. If this happens too quickly, it 



70 



MAINTENANCE RATIONS OF FARM ANIMALS. 



may even lead to congestion of the latter. The process is analogous 
to the closing of the windows of a room as the weather grows colder. 

There is evidently a limit to this method of regulation. If the 
windows are entirely closed nothing more can be effected in this 
manner, and if the weather continues to grow colder the fire in the 
room must be increased. So if the external demand for heat becomes 
so great as to exceed the limits of adjustment in the body more fuel 
material is katabolized — that is, more heat is produced. This was 
first demonstrated by Carl Voit, who obtained the following results 
for the excretion of carbon dioxid by a man at various temperatures : 

Influence of external temperature on metabolism of man — Carl Voit. 



Tempera- 
ture. 


Carbon 
dioxid. 


Urinary 
nitrogen. 


Tempera- 
ture. 


Carbon 
dioxid. 


Urinary 
nitrogen. 


° C. 


Grams. 


Grams. 


°C. 


Grams. 


Grams. 


4.4 


210.7 


4.23 


23.7 


164.8 


3.40 


6.5 


206.0 


4.05 


24.2 


166.5 


3. 34 


9.0 


192.0 


4.20 


26.7 


160.0 


3.97 


14.3 


155.1 


3.81 


30.0 


170.6 




16.2 


158.3 


4.00 









Later and more comprehensive experiments with animals hy Rubner have 
given corresponding results. Thus with two guinea pigs the following figures 
were obtained in 24-hour experiments : l 



Influence of external temperature on metabolism — Rubner. 



Mature animal. 


Young animal. 


Tempera- 
ture of air. 


Tempera- 
ture of 
animal. 


CO 2 per 
kilogram 
and hour. 


Tempera- 
ture of air. 


Tempera- 
ture of 
animal. 


C02 per 
kilogram 
and hour. 


°C. 


11.1 
20.8 
25.7 
30.3 
34.9 
40.0 


°a 

37.0 
37.2 
37.4 
37.0 
37.7 
38.2 
39.5 


Grams. 
2. 905 
2. 151 
1.766 
1..540 
1.317 
1.273 
1.454 


°C. 


10 

20 
30 

35 


°C. 
38.7 
38.6 
38.6 
38.7 
39.2 


Grams. 
4. 500 
3.433 
2. 283 
1.778 
2. 266 



A later experiment by Rubner 2 upon a dog, in which the heat production was 
measured by a calorimeter, gave the following results : 





Heat pro- 


Tempera- 


duction 


ture of air. 


per 




kilogram. 


C. 


Calorics. 


7.6 


83.5 


15.0 


63. 


20.0 


53.5 


25.0 


54. 2 


30.0 


56.2 



1 Biologische Gesetze, p. 13. 



-Arehiv fur Hygiene, vol. 11, p. 285. 



FEED CONSUMPTION A SOURCE OF HEAT. 



71 



CRITICAL TEMPERATURE. 

It is clear from the foregoing results that when the external tem- 
perature falls below a certain limit the heat production of the animal 
shows a marked increase. This point at which the physical regula- 
tion gives way to or begins to be supplemented by the chemical regu- 
lation has been called the " critical temperature " for the animal. 
Above this temperature the radiating capacity of the body surface 
is varied to meet the varying conditions; below it this method of 
regulation is largely exhausted, and therefore the heat production 
is varied to suit the needs. This latter so-called chemical regulation 
is probably effected largely in the muscles, either by visible motion 
or by increase in the muscular tonus, either of which involves an 
increased heat production. This has been clearly shown to be true 
of man and probably applies also to other animals. Above the 
critical temperature there appears to be a slight increase in the heat 
production with rising temperature, probably due to the additional 
energy required for the various processes of physical regulation. 

Any conditions tending to facilitate the escape of heat from the 
body would obviously act like a fall of temperature. Wind, for ex- 
ample, by removing the layer of partially warmed air next to the 
skin, tends to remove the heat more rapidly from the body, so that 
the cold is felt more severely on a windy day, while, on the other 
hand, the effect of a high temperature is modified by wind. A high 
percentage humidity of the air on a warm day hinders the removal of 
heat by evaporation, so that a moist heat is more trying than a dry 
heat. Cold, moist air, on the other hand, facilitates the escape of heat 
from the body by increasing the conducting power of the clothing, 
hair, or fur, so that a damp cold is more severe than a dry cold. The 
direct rays of the sun may impart a considerable amount of heat to 
the body, thus moderating the effect of low temperature and, on the 
other hand, increasing that of high temperature. 

FEED CONSUMPTION A SOURCE OF HEAT. 

For the sake of simplicity, the foregoing paragraphs have dealt 
especially with the case of the fasting animal, neglecting one im- 
portant source of heat, viz, the consumption of feed. As was show T n 
on pages 19-28, the latter results in increasing the katabolism of the 
body, and whether this be considered the result of the work of digestion 
or simply designated as specific dynamic effect, the fact is established 
beyond question. This heat, however, once generated, while unavail- 
able for the physiological processes of the body is just as useful as ex- 
ternal heat for keeping it warm. In other words, the consumption of 
feed will tend to have the same effect as a rise of external tempera- 



72 



MAINTENANCE RATIONS OF FARM ANIMALS. 



ture. This being the case, it is clear that at temperatures consider- 
ably below the critical temperature, all the metabolizable energy of the 
feed will be of use to the body. Part of it will be available for 
physiological uses as already explained, but the remainder, while not 
available in this sense will nevertheless be of use as a source of heat. 

ISODYNAMIC REPLACEMENT. 

It was upon his earlier experiments (published in 1883) made un- 
der substantially the conditions just indicated that Rubner based 
his famous law of isodynamic replacement of nutrients which has, 
played a large part in the discussion of nutrition problems. This 
law may be briefly stated as follows: In amounts less than a main- 
tenance ration the nutrients replace each other or body tissue in in- 
verse proportion to their metabolizable energy. The quantities which 
thus replace each other are accordingly said to be isodynamic. It 
need scarcely be pointed out that the minimum of protein required 
for the maintenance of the nitrogenous tissues is not included under 
this law. Rubner was careful to limit the law to small amounts of 
food. In his earlier publications he stated that it holds only below 
the maintenance ration ; somewhat later he asserted 1 that it obtains 
up to an excess of about 50 per cent over the maintenance requirement. 

These results of Rubner's have passed into the literature of physi- 
ology and are still largely interpreted as representing the relative 
values of nutrients, while Rubner's factors for the metabolizable 
energy of nutrients have been extensively used in computing the 
energy values not only of human dietaries but of stock rations as 
well. Historically, Rubner's earlier investigations mark an epoch 
in the science of nutrition. While similar views had previously 
been advanced by others, Rubner appears to have been the first to 
investigate the subject experimentally. The conception that the 
replacement values of the nutrients could be measured by the rela- 
tive contributions of energy which they make to the activities of 
the body was a contribution of the first order to the study of nutri- 
tion problems, but the exact form given it in these earlier experi- 
ments proves to have been but a partial expression of the truth, as 
Rubner's own later experiment, as well as those of others, have fully 
demonstrated. (Compare pp. 26-28.) 

RELATION OF MAINTENANCE RATION TO CRITICAL TEMPERATURE. 

When its surroundings are above the critical temperature, the 
animal is producing a surplus of heat as a consequence of its neces- 
sary physiological activities and disposes of it by the processes of 



1 Biologisehe Gesotze, p. 20. 



CKITICAL TEMPERATURE. 



73 



physical regulation already described. The heat produced is then in 
a sense an excretum, and under these conditions obviously the ex- 
ternal temperature does not materially affect the maintenance ration. 
The latter, as already shown, is measured by the amount of available 
energy necessary to support the vital processes, i. e,, by the total 
fasting katabolism. 

Below the critical temperature, however, the conditions are differ- 
ent. At relatively low temperatures all the metabolizable energy of 
the feed is used directly or indirectly to keep the animal warm, and 
as the external temperature falls, either more feed must be given or 
more tissue burned to supply the additional heat required to main- 
tain the body temperature. 

FEED CONSUMPTION LOWERS THE CRITICAL TEMPERATURE. 

Since feed consumption is itself a source of heat, the animal con- 
suming feed can, other things being equal, withstand a lower tem- 
perature than when fasting, and the larger the amount of feed 
consumed the lower is the corresponding temperature. The matter 
may also be put in the reverse way. For any particular (low) tem- 
perature there is a certain amount of feed the digestion and assimila- 
tion of which will yield an amount of heat sufficient to supplement 
that derived from the fasting katabolism, so as to just maintain the 
body temperature. This particular external temperature, then, is 
the critical temperature for that amount and kind of feed, and, con- 
versely, that particular ration may be called the critical amount of 
feed for the particular external temperature. 

CRITICAL TEMPERATURE FOR FARM ANIMALS. 

The critical temperature for farm animals has not been definitely 
determined. In the case of cattle and probably of sheep, however, it 
is apparently rather low for animals consuming an ordinary ration. 
Thus Armsby and Fries have found that at about 18° C. the ration 
of cattle can be reduced considerably below the maintenance require- 
ment without any evidence of increased oxidation of tissue for the 
sake of heat production. In the case of fattening animals consuming 
heavy rations and therefore producing a large amount of heat as a 
result of digestive work, the critical temperature would be still lower 
and experiments upon such animals have shown that they may be 
exposed to comparatively low temperatures, as in an open shed or 
yard, without causing them to oxidize any more food material. As 
already stated (p. 56) the critical temperature for the horse appears 
to be relatively higher. 



74 



MAINTENANCE RATIONS OF FARM ANIMALS. 



THE PROTEIN REQUIREMENT FOR MAINTENANCE. 

PROTEIN KATABOLIZED DURING EASTING. 1 

It has already been shown on pages 11-12 that in the previously 
well-nourished fasting animal the katabolism of protein supplies 
but a small part of the total energy required for the support of the 
vital functions. As a preliminary to the consideration of the protein 
requirement, however, some further consideration of the protein 
katabolism during fasting is desirable. 

INFLUENCE OF PREVIOUS FEED. 

The classic experiments of Carl Voit upon fasting dogs showed 
that while the protein katabolism in the early da} T s of fasting may 
vary widely according to the previous feed, it soon falls to a com- 
paratively low level which is approximately the same for the indi- 
vidual animal whatever its amount upon the initial days. This 
behavior is well illustrated by the following results, all upon the 
same animal, which have been fully confirmed by numerous subse- 
quent experiments. 2 

Protein katabolism of fasting dog — Voit. 





2,500 grams 
meat. 


1,800 grams 
meat; 250 
grams fat. 


1,500 grams 
meat. 


1,500 grams 
meat. 


Bread. 


Urinary nitrogen 3 per day: 

Last day of feeding 

First day of fasting 

Second day of fasting 

Third day of fasting 

Fourth day of fasting 

Fifth day of fasting 

Sixth day of fasting 

Seventh day of fasting 


Grams. 
84.4 
28.1 
11.6 
8.9 
8.1 
5.7 
6.2 
5.8 
4.7 


Grams. 
60.7 
17.5 
10.9 
7.8 
6.9 
5.9 
6.0 
5.6 


Grams. 
51.7 
13.9 
8.5 
8.2 
7.0 
6.6 
6.1 
5.6 
6.0 


Grams. 
51.7 
12.4 
8.7 
7.3 
7.0 
6.9 
6.0 
6.0 
5.6 
5.6 
5.3 


Grams. 
11.5 
9.1 
7.3 
7.0 
6.2 
5.9 
6.1 


Eighth day of fasting 

Ninth day of fasting 








Tenth day of fasting 












i 







FASTING KATABOLISM VARIABLE. 



It is not true, however, as is sometimes loosely stated, that the 
protein katabolism of a fasting animal is a constant quantity. On 
the contrary, in the presence of an adequate amount of body fat, its 
amount tends to diminish with the progress of fasting. This fact 
appears more or less clearly in the foregoing experiments, while in 
later ones it is quite marked. For example, in the experiments by 

1 Compare references on p. 8. 
2 Zeitschrift fur Biologie, vol. 2, p. 307. 

3 Computed from Voit's figures for urea. In earlier experiments upon the protein 
metabolism the urea in the urine, as determined by Liebig's titration method, was com- 
monly taken as the measure of protein katabolism. Later experience has shown that 
these results are not strictly accurate, but the amount of urea under such circumstances 
is so nearly proportional to the total urinary nitrogen that the results as given above are 
entirely adequate as an illustration of the point under discussion. 



THE MINIMUM OF PROTEIN. 



75 



Benedict, cited on page 15 in illustration of the relative constancy of 
the energy katabolism, the total protein katabolism showed a distinct 
falling off, and the same is true in less degree when computed per 
kilogram weight. The total urinary nitrogen upon the several days 
of the experiment was : 



Protein katabolism of fasting man — Benedict. 



Days. 


Urinary nitrogen. 


Days. 


Urinary nitrogen. 


Total. 


Per kilo- 
gram 
weight. 


Total. 


Per kilo- 
gram 
weight. 


1 


Grams. 
12. 24 
12.45 
13.02 
11.63 


Gram. 
0.206 
.211 
.223 
.202 


5 


Grams. 
10. 87 
10. 74 
10.13 


Gram. 
0. 191 
.190 
.181 


2 


6 


3 


7 


4 





E. and O. Freund 1 determined the daily nitrogen excretion of Succi, a pro- 
fessional faster, with the following results: 



Protein katabolism of fasting man — E. and O. Freund. 



Days. 


Nitrogen. 


Days. 


Nitrogen. 


Days. 


Nitrogen. 


1 


Grams. 
17.0 
11.2 
10.55 
10.8 
11.19 
11.01 i 
8.79 j 


8 


Grams. 
9.74 
10.05 
7. 12 
6.23 
6.84 
5.14 
4. 66 


15 


Grams. 
5.05 
4. 32 
5.4 
3.6 
5.7 
3.3 
2. 82 


2 


9 


16 


3 


10 


17 


4 


11 


18 


5 


12 


19 


6.. 


13 


20 


7 


14 


21 









A similar phenomenon was observed by Michaud in experiments on the rela- 
tive value of proteins described on a subsequent page. A dog, after 44 days ab- 
stinence from protein (16 days without food followed by 2S on nonnitrogenous 
food), excreted daily 1.42 grams nitrogen. The same dog after prolonged feeding 
upon low protein rations, however, showed in a three-days fast an average daily 
excretion of only 0.95 grams nitrogen. On the other hand, however, as already 
pointed out, the fasting protein katabolism may show a very marked increase 
with the progress of fasting in the absence of a sufficient store of body fat. 
It appears, then, that in fasting the protein katabolism is much more variable 
in amount than the total katabolism, and this fact must be remembered in any 
discussion of the protein requirement. 

THE MINIMUM OF PROTEIN. 2 

It is evident that the comparatively small amount of protein kata- 
bolized in the fasting animal so long as its store of fat is reasonably 
abundant is at least all that is absolutely essential to the vital 

1 Cited by Lusk. 

2 For a more exhaustive discussion of the subjects of this and succeeding paragraphs, 
including references to the literature, compare the references on page 8, in particular 
Magnus-Levy, pp. 198-423 ; Tigerstedt, pp. 391-480 ; Lusk, Chapters IV and V. 



76 



MAINTENANCE RATIONS OF FARM ANIMALS. 



processes, since the latter go on for a considerable time in a sub- 
stantially normal manner. The question at once arises whether this 
fasting katabolism represents the amount of digestible protein which 
must be supplied in the feed in order to maintain the protein tissues 
of the body. 

INFLUENCE OF NONNITROGENOUS MATERIALS. 

In the first place, it is to be remarked that, as just shown, the 
protein katabolism during fasting is by no means a fixed and definite 
quantity, but may var}^ even in the same individual within quite 
wide limits both absolutely and as regards the proportion of the 
total energy requirement which is supplied by it. From the results 
cited on pages 12-13, it is evident that a most important factor 
influencing the fasting katabolism is the stock of fat in the body 
and that when the latter is reduced protein is katabolized for the 
sake of its energy. In other words, a lack of readily available non- 
nitrogenous material in the body tends to increase the protein 
katabolism above its minimum value. Evidently, then, in seeking 
to determine the minimum amount of protein required for main- 
tenance, the food given should contain a liberal supply of non- 
nitrogenous nutrients to supply the necessary energy for the animal, 
since otherwise there is danger that the protein will be katabolized 
for this purpose, resulting in an apparent increase of the maintenance 
requirement. 

RELATION TO FASTING KATABOLISM. 

In the early experiments upon this subject, especially those of Voit, the full 
significance of this fact had not been recognized. His experiments, in which 
increasing amounts of protein alone were fed (compare p. 79), showed that 
protein equal to two and a half to three times the fasting katabolism was 
necessary to reach nitrogen equilibrium, and this result was generalized and 
passed current for a considerable time. 

Munk 1 seems to have been the first to challenge this view and to claim not 
only that an amount of protein equal to that katabolized during fasting is 
adequate, but that with an abundant supply of nonnitrogenous material, espe- 
cially carbohydrates, in the feed a notably smaller amount of protein is suffi- 
cient to maintain the nitrogen balance. Munk's experiments either include no 
comparison with the fasting katabolism of the same animal or a comparison 
not in all respects satisfactory, but they show clearly that nitrogen equilibrium 
was maintained on a supply of protein less than that usually found to be 
katabolized in similar fasting animals. 

On the other hand, extensive experiments by Voit and Korkunoff 2 on dogs 
led these experimenters to an opposite conclusion. Starting with a ration 
deficient in protein but containing a very liberal supply of nonnitrogenous 
nutrients, the protein of the feed was gradually increased until an amount was 



Wirchow's Archiv fur Pathologische Anatomie und Phj T siologie und fur Klinische Medi- 
zin, vol. 101, p. 91 ; vol. 133, Supp. ; vol. 132, p. 91. Archiv fur (Anatomie und) Pbysi- 
ologie, 1896, p. 183. 

2 Zeitschrift fur Biologie, vol. 32, p. 58 



THE MINIMUM OF PROTEIN. 



77 



reached sufficient to produce equilibrium between the income and outgo of 
nitrogen. Two series of experiments were performed, in one of which the non- 
nitrogenous nutrients consisted chiefly of fat, and another in which they con- 
sisted of carbohydrates. Considering only those experiments in which the feed 
consumed was more than sufficient in amount to supply the estimated demand 
of the body for energy, it was found that when the nonnitrogenous nutrients 
consisted of fat the nitrogen (protein) of the feed had to be increased to ap- 
proximately 130 per cent of the amount katabolized in fasting before nitrogen 
equilibrium was reached — that is, before the stock of body protein was main- 
tained. When, however, the energy demands of the body were supplied by 
carbohydrates instead of fats, a supply of nitrogen (protein) in the feed equal 
to or even somewhat less than the amount katabolized in fasting sufficed to 
insure nitrogen equilibrium. 1 Cremer and Henderson, 2 in experiments on a 
dog with a ration estimated to supply the necessary energy for maintenance, 
were unable to maintain nitrogen equilibrium on even as small an amount as 
did Yoit and Korkunoff. 

In the case of man, on the other hand, numerous experiments seem to have 
demonstrated that an amount of feed protein notably less than the ordinary 
fasting katabolism is sufficient to maintain nitrogen equilibrium, although 
even in this case the comparison in nearly every case is with the average 
fasting katabolism and not with that of the individual under experiment. 
This average for man, however, has been well established by numerous experi- 
ments and seems not to vary widely for individuals, while in Benedict's ex- 
periments 3 upon nutrition after fasting a material diminution of the protein 
katabolism of the subject was observed on the second and third days. In every 
case the body lost protein, but in experiments 70 and 74 there was a storing up 
of energy. 

Protein katauolis?n during and after fasting.' 1 



Experi- 
ments 69 
and 70. 



Experi- 
ments 71 
and 72. 



Fasting: 

First day 

Second day . . 

Third day.... 

Fourth day . . 

Fifth day 

Sixth day 

Seventh day . , 
Food after fasting: 

First day 

Second day . . 

Third day.... 



Grams. 
60.5 
85.6 
90.2 



Grams. 
35.0 
66.2 
78.6 
64.4 




Experi- 
ments 73 
and 74. 



Grams. 
61.7 
71.8 
69.2 
62.3 
59.9 



64. 44 
49. 50 
40. 68 



Experi- 
ments 75 
and 76. 



Grams. 
73.4 
74.7 
78.1 
69.8 
65.2 
64.4 
60.8 

61.02 
42. 90 
46. 92 



Another factor which must be taken into consideration in fixing the minimum 
of protein is what may be called the time element. Eubner calls attention 
to the fact that if the protein of the ration is consumed at a single meal there 
may be for a time a surplus of protein or its digestive products in the system, 

1 Yoit and Korkunoff put a different interpretation upon their results, basing it upon 
the fact that a certain portion of the urinary nitrogen is derived from the nitrogenous 
extractives of the flesh metabolized in the body. Compare the account of their experi- 
ments in the writer's Principles of Animal Nutrition, pp. 135-139. 

2 Zeitschrift fur Biologie, vol. 42, p. 612. 

3 Loc. cit., pp. 456 and 529. 

4 The odd-numbered experiments were the fasting experiments. The even-numbered are 
those in which food was given and which immediately followed the corresponding fasting 
experiments. 



78 



MAINTENANCE .RATIONS OF FARM ANIMALS. 



while at a subsequent period of the day there inay be a deficiency which will 
be made good by a draft upon the proteins of the tissues. 

For the purpose of this discussion, it is unnecessary to pursue 
further the somewhat complicated question of the absolute pro- 
tein minimum and its relations to the fasting protein katabolism. 
especially in view of the fact that, as has been shown, the latter is 
itself more or less variable. It appears well established that on a diet 
containing an abundance of carbohydrates a supply of protein 
equivalent to the fasting protein katabolism is sufficient to meet the 
needs of the organism, while it is possible that a less amount will 
suffice. Fats appear to be distinctly less efficient than carbohydrates 
in keeping the protein katabolism at the minimum. Precisely why 
this is the case has not been fully made out, although Landergren 1 
has advanced the explanation that a minimum of carbohydrates is 
essential to the chemical processes of metabolism and that when a 
sufficient amount is not supplied in the feed, protein is katabolized 
for the sake of producing carbohydrates, with the result that on a 
low protein diet nitrogen katabolism is increased. In any case, it 
is clear that the protein requirement upon a mixed ration sufficient 
in quantity is comparatively small. 

EFFECT OF SURPLUS OF PROTEIN. 
INCREASES PROTEIN KATABOLISM. 

But while a relatively small quantity of digestible protein is suffi- 
cient, in the presence of an abundant supply of fuel material, to main- 
tain the body in nitrogen equilibrium, an increase of the feed protein 
above this minimum does not result in any large or long- continued 
gain of protein tissue by the mature animal, but causes a correspond- 
ing increase in the protein katabolism, as is shown by the prompt 
increase in the amount of nitrogen excreted in the urine. 

This fact was demonstrated more than 50 years ago by C. Voit, in collabora- 
tion at first with Bischoff 2 and later alone and with Pettenkofer, 3 in experiments 
on carnivorous animals, and almost innumerable subsequent investigations have 
shown that it is true not only of these animals, but of man and of herbivorous 
animals as well. The protein katabolism is determined chiefly by the supply 
of digestible protein in the feed, and the body comes quite promptly 
into equilibrium with any amount above the maintenance requirement which 
can be consumed, the nitrogen of the excreta substantially equaling that of the 
feed. This is well illustrated by the following selection from Bischoff and 
Voit's results upon a dog, 4 arranged in the order of the amount of protein 
eaten. 

1 Jahresbericht iiber die Forschritte der Tier-Chemie, vol. 32, p. 685. 

2 Gesetze der Ernahrung des Fleischfressers, 1860. 

8 Published chiefly in the Annalen der Chemie und Pharmacie and the Zeitschrift fur 
Biologie. See also Voit : " Physiologie des Stoffwechsels," in Hermann's Handbuch der 
lMiysiologie. 

4 Voit's compilation, Zeitschrift fur Biologie, vol. 3, p. 5. 



EFFECT OF SURPLUS OF PROTEIN. 
Daily protein katabolism of dog — Bischoff and Voit. 



79 



Meat 
eaten. 


Nitrogen 
of feed.i 


Nitrogen 
excreted in 
urine. 2 


\X 1 initio. 


KxTCLTflS . 


Grams. 


176 


6.0 


12. 6 


300 


10. 2 


1 /I Q 


480 


16. 3 


16 3 


500 


17. 


18 7 


600 


20^4 


22! 9 


800 


27.2 


26 1 


900 


30.6 


31.7 


1,000 


34.0 


35.9 


1,200 


40.8 


41.1 


1,500 


51.0 


49.5 


1,800 


61.2 


59.7 


1,900 


64.6 


64.9 


2,000 


68.0 


67.2 


2,200 


74.8 


71.9 


2,500 


85.0 


80.7 


2,660 


90.4 


84.5 



Dates. 



Nov. 26 to 27, 1858.... 

Nov. 24 to 25 

May 1 to 4, 1864 

Apr. 20 to June 1 , 1863 
Nov. 22 to 23,1855.... 
Feb. 13 to 17, 1865.... 
Nov. 20 to 21,1858.... 

Apr. 14 to 20,1863 

Nov. 18 to 19,1858.... 

Apr. 1 to 14,1863 

Mar. 25 to Apr. 1, 1859 

Apr. 5, 1858 

June 21 to 29, 1863.... 

Jan. 22 to 25,1858 

Dec. 5 to 7, 1858 

Jan. 25, 1858 



Moreover, what has been shown to be true of an exclusively protein diet is 
substantially true also of one containing liberal amounts of fats or carbo- 
hydrates. Thus in the following selection from Bischoff and Voit's experiments 1 
bearing upon this point it is clear that, notwithstanding the presence of con- 
siderable amounts of fat in the feed, the protein katabolism, as measured by 
the urinary nitrogen, increased substantially in the same ratio as the protein 
supply. 

Daily protein katabolism of dog — Bischoff and Voit. 



Dates (inclusive). 


Eeed. 


Nitrogen 
of feed. 2 


Urinary 
nitrogen. 3 


Fat. 


Lean meat. 




Grams. 


Grams. 


Grams. 


Grams. 


Nov. 22 to Dec. 1, 1857 


250 


150 


5.1 


7.3 


Dec. 2,1857 


250 


250 


8.5 


8.9 


Dec. 5, 1857, to Jan. 5, 1858 


250 


500 


17.0 


14.4 


Jan. 9 to 11,1868 


250 


1.000 


34.0 


28.3 


Jan. 15 to 18, 1858 


250 


1,500 


51.0 


45.9 


Apr. 1 to 7, 1859 


250 


1,800 


61.2 


56.4 


Jan. 13 to 14, 1859 


250 


2,000 


68.0 


63.4 



Carnivorous animals have been extensively used in the investigation of such 
questions as the foregoing, and others which are to be discussed later, largely 
because with them it is possible to employ a diet consisting of but one or two 
simple nutrients, but the main facts which have been brought out by such in- 
vestigations have been shown to be true also of herbivorous animals. In the 
latter, as in the carnivora, the protein katabolism is determined chiefly by the 
supply of protein in the feed. 

As early as 1852, eight years before the publication of Bischoff and Voit's 
inevstigations, Lawes and Gilbert, 4 in discussing the results of theri fattening 
experiments upon sheep and pigs, called attention to the very wide variations 



1 Gesetze der Ernahrung des Fleischfressers, 1860, pp. 97-115. 

2 Average of nitrogen of lean meat, 3.4 per cent. 

3 Computed from urea. 

i Report British Association for the Advancement of Science, 1852, Rothamsted 
Memoirs, Vol. II. 



80 MAINTENANCE RATIONS OF FARM ANIMALS. 

in the amount of protein consumed, both per unit of weight and especially 
per unit of gain, and concluded that the apparent excess of protein in some 
cases must have served substantially for respiratory purposes. 

Of the numerous later and more specific investigations on herbivora in which 
the nitrogen excretion has been determined, the following 1 may serve as an 
example. Two sheep were fed in periods 1 and 7 a basal ration of hay and 
barley meal. To this ration were added in the intermediate periods varying 
amounts of nearly pure protein in the form of conglutin (of lupins) or of 
flesh meal. A comparison of the nitrogen digested from the ration with the 
urinary nitrogen shows that the latter increased and diminished substantially 
parallel with the former. 



Protein kataboUsm, of sheep per day and head — Henneberg and Pfeiffer. 





Sheep I. 


Sheep II. 




Nitrogen 


Nitrogen 


Nitrogen 


Nitrogen 




digested. 


in urine. 


digested. 


in urine. 




Grams. 


Grams. 


Grams. 


Grams. 


Period 1 


8.18 


7.48 


7.81 


6.98 


Period 2 


17.86 


16. 82 


17.72 


16.37 


Period 3 


27.22 


25.75 


27.33 


23.94 


Period 4 


36.99 


32. 71 


37.07 


32.09 


Period 5 


26.76 


25.63 


26.91 


24.54 


Period 6 


17.62 


16.64 


16.94 


15.99 


Period 7 


8.34 


8.06 


8.00 


7.62 



UTILIZATION OF PROTEIN LIMITED. 

That the mere giving of protein food can not cause a large storing 
up of protein is indeed sufficiently obvious from daily experience. 
The muscles of the weakling can not be converted into those of the 
athlete by feeding him upon a meat diet, nor the small man increased 
in size by a very abundant protein supply. The protein tissues of 
the mature animal have reached their natural limit of size and con- 
sequently the capacity of the body to store up protein is limited, in 
such an animal, beyond the minimum required to make good the 
necessary katabolism in the cells protein can be utilized only to a 
small extent in the body as protein, and it is therefore rapidly 
katabolized, its nitrogen appearing in the urine as urea and other 
familiar end products. Nor is the situation essentially different in 
the growing or the milk-producing animal. While these animals are 
able to utilize considerable amounts of feed protein, yet the limit of 
this utilization is set by the normal rate of growth of the protein 
tissues or the capacity of the mammary glands to manufacture the 
casein and other proteins of the milk. Any surplus of protein over 
the amount which can be used for this purpose is katabolized pre- 
cisely as is a surplus over the very small demand of the mature 
animal. 



1 Henneberg and Pfeiffer. Journal fiir Landwirtschaft, vol. 38, p. 215. 



PROTEIN AS A SOURCE OF ENERGY. 



81 



As a single striking example there may be cited an experiment by Jordan, 1 in 
which the protein supply of cows, beginning with a liberal ration, was gradually 
diminished to about one-half and then gradually increased again to the original 
amount. The following table shows the average nitrogen balance of cow No. 12 
of the second series of experiments, the daily results being grouped into periods 
as indicated. 

Average daily nitrogen balance of cows — Jordan. 



Date. 


Number 
of days. 


Nitrogen 
digested. 


Nitrogen 
of milk. 


Nitrogen 
of urine. 


Gain by 
body. 






Grams. 


Grams. 


Grams. 


Grams. 


Jan. 30 to Feb. G 




186.6 


81.7 


87.0 


+17.9 


Feb. 6 to 16 


10 


18-5.2 


81.4 


87.5 


+16.3 


Feb. 16 to 26 


10 


161.6 


77.5 


81.9 


+ 2.2 


Feb. 26 to Mar. 8 


10 


130. 8 


74.0 


56.5 


+ .3 


Mar. 8 to 18 


10 


117.2 


66.6 


43.7 


+ 6.9 


Mar. 18 to 28 


10 


143. 6 


69.6 


61.8 


+12.2 


Mar. 28 to Apr. 7 


10 


171.4 


71.6 


89.2 


+10.6 


Apr. 7 to 14 


7 


185.7 


71.9 


104.4 


+ 9.4 



The amount of milk protein, like the total milk solids, diminished in quite a 
normal way with the advance in lactation, while the percentage of protein in 
the solids remained about the same. On the low protein rations of the middle 
periods there seems to have been some falling off in the amount of milk protein 
produced (and of the total milk solids as well) in comparison with what might 
have been expected on an unchanged ration, but the difference is small, except 
in one or two periods where the protein supply reached the lowest limit. Aside 
from this the principal effect of the variations in the amount of digestible pro- 
tein supplied was to increase or diminish the amount of urinary nitrogen, which, 
as the table clearly shows, rose and fell with the supply of nitrogen in the feed. 

PROTEIN AS A SOURCE OF ENERGY. 

This increased katabolism of protein, however, is not to be re- 
garded as a total loss of so much food material. The manner in 
which surplus protein is disposed of is rendered clear by a considera- 
tion of the chemistry of protein katabolism. Proteins are resorbed 
from the digestive tract in the form of comparatively simple cleav- 
age products, chiefly amino-acids, and the body uses these nitroge- 
nous cleavage products as building stones out of which to reconstruct 
body proteins broken down in the vital processes. As has just 
been shown, however, this necessary demand is relatively small, wmile 
the mature animal has lost the capacity which it had during growth 
of building up large amounts of new protein tissue. When the 
blood is, so to speak, flooded with these amino-acids in high protein 
feeding, some increase in the formation of body protein appears to 
result, as will be shown immediately, but this consumes a relatively 
small proportion of the nitrogenous matter and lasts for only a 
limited time. It is obviously an advantage to the organism, there- 
fore, to be able to dispose of the surplus nitrogen. This it accom- 
plishes by splitting off the NH 2 group and excreting it in the form 



1 New York Agricultural Experiment Station. Bulletins 132 and 197. 
8489°— Bull. 143—1 2 6 



82 



MAINTENANCE RATIONS OF FARM ANIMALS. 



of urea, etc., leaving a nonnitrogenous residue which contains the 
larger portion of the chemical energy of the protein which it repre- 
sents and is in condition to be oxidized as fuel material. (Compare 
pp. 30-32.) 

The increased nitrogen excretion on a high protein diet is sinrply 
the method by which the organism gets rid of useless nitrogen, while 
retaining the larger share of the energy of the protein for fuel 
purposes. In other words the organism when confronted with a 
protein supply in excess of its needs is able by what seems to be a 
comparatively simple process to transform it into nonnitrogenous 
fuel material with but slight loss, getting rid of the useless nitrogen 
as urea through the urine. The increased nitrogen excretion conse- 
quent on high protein feeding does not mean the total destruction 
of the corresponding amount of protein, but simply its transforma- 
tion into compounds which can serve as sources of energy. 

STORAGE OF PROTEIN. 

In the mature animal a surplus of feed protein is largely katabo- 
lized, so that a continued increase of the protein tissue of the animal 
can not be brought about, as can that of the adipose tissue, simply 
by a surplus in the feed. The protein content of such an animal, 
however, is not to be regarded as absolutely fixed, so that the protein 
supply has no effect upon it. On the contrary, a considerable range 
of variation is possible. 

When the protein supply is increased, nitrogen equilibrium is not established 
at once, but for a time more or less storage of nitrogenous material takes place. 
For instance, when a dog in Voit's experiments 1 was changed from a ration 
of 500 grams of meat daily for 42 days to one of 1,500 grams, the urinary nitro- 
gen showed the following behavior on the last three days of old feeding and on 
the first seven of the new : 



Storage of protein by dog — Toit. 





Date. 


Meat fed. 


Nitrogen 
of feed. 


Nitrogen 
of urine. 2 


Gain of 
nitrogen. 




1863. 


Grams. 


Grams. 


Grams. 


Grams. 




May 29 


500 


17.0 


18.9 


-1.9 


Experiment No. 40 


- May 30 


500 


17.0 


18.2 


-1. 


May 31 


500 


17.0 


17.7 


- .7 




June 1 


1,500 


51.0 


41.1 


+9.9 




June 2 


1,500 


51.0 


44.1 


+6.9 




June 3 


1,500 


51.0 


46.9 


+4.1 




June 4 


1,500 


51.0 


48.0 


+3.0 


June 5 


1,500 


51.0 


48.6 


+2.4 




June G 


1,500 


51.0 


48.9 


+2.1 




June 7 


1,500 


51.0 


50.6 


+ -4 



Upon the lighter ration the animal was losing a small amount of protein 
daily. On the heavier ration there was a diminishing gain for six days, ap- 



1 Zeitsehrift fur Biologie, vol. 3, p. 80. 

2 Computed from Voit's figures for urea. 



FLUCTUATIONS IN BODY PROTEIN. 



83 



proximate equilibrium being reached on the seventh day. The total gain in the 
seven days was 28.8 grams nitrogen, equivalent to 847 grams of fresh flesh, or 
about 12 per cent of the surplus fed, equivalent to from 3.5 to 4 per cent of the 
amount probably present in the body of the 35-kilogram dog. 

In order to retain this protein which was stored up in the body, however, it 
was necessary to continue the heavier ration of 1,500 grams of meat. When, 
in previous periods of the same series, a ration of 1,500 grams of meat was fol- 
lowed by one of 1,000 grams and this by one of 500 grams, the protein pre- 
viously stored up was rapidly katabolized again, as the following table shows : 



Loss of protein by dog — Voit. 





Date. 


Meat fed. 


Nitrogen 
of feed. 


Nitrogen 
of urine. 1 


Gain of 
nitrogen. 




1863. 


Grams. 


Grams. 


Grams. 


Grams. 




Apr. 


11 


1,500 


51.0 


48.4 


+2.6 


Experiment No. 38 (last 3 days) 


Apr. 


12 


1,500 


51.0 


50.9 


+ .1 


Apr. 


13 


1,500 


51.0 


52.8 


-1 8 




Apr. 


14 


1,000 


34.0 


38.6 


-4.6 




Apr. 


15 


1,000 


34.0 


36.4 


-2.4 


Experiment No. 39 


Apr. 
Apr. 


16 
17 


1,000 
1,000 


34.0 
34.0 


36.4 
36.1 


-2.4 
-2.1 




Apr. 


18 


1,000 


34.0 


34.3 


— .3 




Apr. 


19 


1,000 


34.0 


35.2 


-1.2 




Apr. 


20 


500 


17.0 


23.7 


-6.7 




Apr. 


21 


500 


17.0 


20.4 


-3.4 


Experiment No. 40 


Apr. 
Apr. 


22 
23 


500 
500 


17.0 
17.0 


20.9 
18.8 


-3.9 
-1.8 




Apr. 


24 


500 


17.0 


17.4 


- .4 




Apr. 


25 


500 


17.0 


18.8 


-l.S 



The total loss of nitrogen from the body for the 12 days included in the 
table is 31 grams, or an amount about equal to that stored up in passing from 
the 500-gram to the 1,500-gram ration. 

This comparatively small store of rapidly katabolizable protein in the body 
after liberal protein feeding Voit designated as circulatory protein, in distinc- 
tion from the large mass of stable protein which he called organ protein. A 
variety of other names, corresponding to more or less definite theories as to 
the nature of the distinction between the two types of protein, have been pro- 
posed by later investigators, such as stable and labile, organized and unorgan- 
ized, tissue and reserve, living and dead, protein. Still others, notably Gruber, 3 
explain the temporary storage of nitrogenous matter in the body as due to a 
lag in the katabolism of protein, so that the splitting off of its nitrogen is not 
complete within the ordinary 24-hour period. The facts, however, that the 
nitrogen excretion follows in general the supply in the feed but that a tempo- 
rary and limited storage of nitrogenous material in the body may result from 
liberal protein feeding, are undisputed. 

FLUCTUATIONS IN BODY PROTEIN. 

It is a familiar fact that a fasting animal may live and continue 
to perform the essential bodily functions for some time, while los- 
ing daily a not inconsiderable amount of protein. To cite a single 
striking example, Rubner observed in a fasting rabbit up to the time 
of death, on the nineteenth day, a loss of 45.2 per cent of the com- 
puted nitrogen of the body. 3 While this is an extreme case, neverthe- 

1 Computed from urea. 

2 Zeitschrift fur Biologie. vol. 42, p. 407. 

3 E. Voit. Zeitschrift fur Biologie, Vol. 41, p. 139. 



84 



MAINTENANCE RATIONS OF FARM ANIMALS. 



less it is evident that there must be a relatively large loss of body 
protein in those more moderate cases in which the deprivation of 
protein is not continued so long as to cause death. Furthermore, 
the losses occurring in these latter cases may be made good by subse- 
quent feeding and the animal restored to its original state. Strik- 
ing examples of the same fact are familiar in the human subject in 
the emaciation due to long illness and the restoration of the body 
during convalescence. Pugliese 1 has shown that a similar storage of 
protein takes place rather rapidly in the liver when a previously 
fasted animal receives feed again. In brief, it is evident that the 
body of the mature animal may fluctuate within somewhat wide limits 
as regards its protein content without necessarily causing any serious 
or permanent derangement of its functions. 

We can hardly suppose such a fluctuation to consist to any large 
extent of an actual destruction and rebuilding of the cells of muscu- 
lar or other tissue, but must regard it as effected chiefly by changes in 
the amount of cell contents — an alternate atrophy and hypertrophy of 
the cells under the influence of the changing protein supply. This 
same conception may be invoked, however, to explain small as well 
as large fluctuations in the body protein. According to Eubner, 2 
the cells of the body seek to maintain an optimum protein content, 
and in proportion as this becomes reduced they show a capacity 
for storing up protein, when a more abundant supply is offered in 
the feed, which is analogous to that observed during growth. On the 
other hand, when the supply of feed protein is insufficient, protein 
previously stored may be katabolized. 

In other words, as regards its stock of nitrogenous material the 
organism may exist and function at a higher or lower level accord- 
ing to the amount of protein supplied in the feed, while for each 
level of protein stock a certain supply in the feed is necessary — that 
is, the protein required for maintenance varies. With carnivora on 
a largely protein diet, such as was used in Voit's experiments, the 
adjustment of the body to the protein supply seems to take place 
rather promptly. In the case of herbivora, however, the adjustment 
appears to be more gradual, possibly owing to the relatively large 
supply of nonnitrogenous ingredients in their feed, and apparently 
some gain of protein may continue for a considerable time, although 
when expressed as a percentage of either the total feed protein or 
of the body protein the gain is relatively small. 

RELATION TO ENERGY SUPPLY. 

The prime demand of the organism is for energy for the per- 
formance of its vital functions, and if necessary it will draw upon 
its own tissues for this purpose. No clear conception of the laws 



1 Jahresbericht fiber die Fortschritte der Tier-Chemie, vol. 34, p. 529. 

2 Das Problem dor Lebensdauer, etc. 



RELATION" TO ENERGY SUPPLY. 



85 



governing the protein metabolism can be reached without taking 
into consideration the energy relations. 

Ordinarily, the nonnitrogenous nutrients of the feed constitute 
the principal source of this energy. The proteins, however, or at 
least the cleavage products of their digestion or transformation, 
readily undergo a process of deamidization by which their nitrogen 
is split off and excreted, leaving a nonnitrogenous residue wmich is 
available as a source of energy. It is evident, then, that the rela- 
tive abundance or scarcity of the supply of nonnitrogenous nutrients 
to the cells of the body may profoundly modify the extent and 
character of the protein metabolism and consequently the magnitude 
of the protein requirement. 

One instance of this effect is the so-called premortal rise of the 
protein katabolism of the fasting animal when the store of body 
fat is reduced below a certain level. (Compare pp. 12-13.) Here 
the relative deficiency of fuel material in the circulation causes an 
increased breaking down of the cell protein, presumably by hydro- 
lytic cleavage and subsequent deamidization, its nitrogen being 
gotten rid of as urea, etc., and the nonnitrogenous residue serving as 
a source of energy in place of the lacking fat. 

A precisely similar thing occurs when the nonnitrogenous nutri- 
ents in the feed are relatively deficient and is especially striking in 
their entire absence. It was pointed out on pages 75-78 that the 
protein katabolism during fasting is at least an approximate measure 
of the minimum protein requirement of the body, and that if this 
amount, or perhaps even less, be supplied in the feed, along with 
an abundance of nonnitrogenous material, the stock of protein in 
the body may be maintained. But if the experiment be made of 
supplying the minimum of protein without nonnitrogenous matter 
a very different result is obtained. 

Tlins in one such experiment by E. Voit and Korkunoff, 1 a fasting dog 
excreted about 4 grams of nitrogen per day, equivalent, of course, to a daily 
loss of about 24 grams of body protein, while in addition to this it must 
have been oxidizing considerable body fat. When, however, it was fed slightly 
more than 24 grams of protein 2 (4.1 grams nitrogen), with no other feed, 
its nitrogen excretion jumped to 5.56 grams per day, so that it was still losing 
daily 1.46 grams of nitrogen, equivalent to 8.76 grams of -protein. Instead of 
the entire amount of protein in the feed being applied to make good the losses 
of protein tissue, over one-third of it was katabolized, its nitrogen appearing 
in the urine and its nonnitrogenous residue doubtless being used as fuel 
material. Protein rather more than equal to the 8.76 grams lost was then 
added to the ration, but again the protein katabolism increased and the 
body failed to maintain its stock of protein, and it was not until protein equal 
to about three times the fasting katabolism was fed that equilibrium was 
reached. The details of the experiments are shown in the following table, 

1 Zeitschrift fur Biologie, vol. 32, p. 67. 

2 In the form of lean meat from which the extractives had been removed by treatment 
with water. 



86 



MAINTENANCE RATIONS OF FARM ANIMALS. 



the results furnishing also a striking illustration of the interesting relations 
between protein supply and protein katabolisin which had been demonstrated 
more than 30 years earlier by the classic experiments of Bischoff and Voit. 



Effect of protein supply on protein TcataboUsm of clog — E. Voit and Korlcunoff. 





Nitrogen in— 


Food. 


Feces and 
urine. 


Gain ( + ) 
or loss( — ). 


Nothing 


Grams. 


4. 10 
5.74 
6.77 
7. 59 
8. 20 
10. 24 
11.99 
15. 58 
13. 68 


Grams. 
3. 996 

5. 558 
6.495 
7.217 
7.804 
8. 726 
10.579 
12.052 
14. 314 
13. 622 


Grams. 
-3. 996 

-1.458 

- .755 

- .447 

- .214 

- .526 

- .339 

- .062 
+ 1.266 
+ .058 


Extracted meat (grams): 

100 


140 


165 


185 


200 ... 


230 


360 


410 


360 





It is clear that in the protein-fed animal, as in the fasting animal, 
the demands of the organism for energy take precedence over the 
need for repair material, and that in default of nonnitrogenous 
material the protein of feed or of tissue is seized upon and katabo- 
iized for this purpose even at the expense of a loss of body protein, 
the body seeming to find it easier to do this than to draw upon the 
stores of fat in the adipose tissues. 

What is so strikingly true in the total absence of nonnitrogenous 
nutrients holds good also in less degree in case of their relative de- 
ficiency. If a portion of the nonnitrogenous nutrients are withdrawn 
from a mixed ration, the protein katabolism usually increases, while, 
on the other hand, if nonnitrogenous nutrients be added to such a 
ration the tendency is to diminish the protein katabolism. This 
well-known influence of the supply of nonnitrogenous nutrients upon 
the protein katabolism, even in an abundant ration, is well illustrated 
by some of Kellner's respiration experiments on cattle, 1 in which 
starch was added to a basal ration. The following table shows the 
average daily gain of nitrogen by the animal on the basal ration and 
the increased gain following the addition of starch. 



Effect of nonnitrogenous nutrients on gain of protein by cattle — Kellner. 



Animal. 


Gain of nitrogen. 


On basal 
ration. 


With addi- 
tion of 
starch. 


Difference. 


OxD 


Grams. 
12. 75 
5. 64 
-.03 


Grams. 
13.71 
20.37 
17. 09 
12.95 
15.05 


Grams. 
+ 0.95 
+20. 73 
+ 17. 12 
+ 5.72 
+ 9.56 


Ox F 


Ox G 


Ox II 

Ox J 


7. 23 
5. 49 



1 Die Landwirtschaftlichen Versuchs-Stationen, Band 53. 



EEL ATI ON TO ENERGY SUPPLY. 



87 



It has been shown that this effect is produced not only by the true 
fats and by the soluble hexose carbohydrates, such as starch and the 
sugars, but likewise, in the case of herbivorous animals, by those ill- 
known ingredients of feeding stuffs, especially of the crude fiber and 
the nitrogen-free extract, which disappear in the passage of the food 
through the alimentary canal and which are commonly spoken of as 
being digested. This statement covers also the organic acids, whether 
resulting from the fermentation of the carbohydrates or contained 
in the feed. 1 

We are not, however, to conceive of a sharp distinction in this 
respect between an insufficiency and a sufficiency of nonnitrogenous 
nutrients, but rather of a tendency on the part of the latter to 
diminish the protein katabolism, a tendency more or less marked 
according to their abundance in the ration. We are not to under- 
stand that no nitrogenous material is katabolized for fuel purposes 
as long as sufficient nonnitrogenous nutrients are present to supply 
the demands for energy, nor that even the largest quantities of 
the latter can prevent the katabolism of protein supplied in excess 
of the possible constructive use by the body. We may believe that 
the protein cleavage products, either derived from the feed or from 
tissue katabolism, are always present in the blood and that more or 
less deamidization is continually going on, resulting in a use of 
protein material as fuel. On the other hand, nonnitrogenous sub- 
stances, derived from the feed or the body fat, are also present and 
take their share in supplying energy. We may probably conceive 
of the quantitative character of the katabolism as being determined, 
in a very broad sense, by the law of mass action. An increase of non- 
nitrogenous materials in the blood or lymph tends to diminish the 
deamidization and subsequent oxidation of the cleavage products 
of protein and through this, secondarily, to diminish the breaking 
down of body protein or to stimulate and prolong the limited storage 
of protein possible in the mature animal. 

As regards the maintenance requirement, it is evident, then, that 
the sufficiency of a given amount of protein depends not only upon 
the plane of protein nutrition of the body, but also upon the amount 
of nonnitrogenous nutrients supplied with the protein. With an 
abundant supply of the former an amount of protein equal to the 
fasting katabolism, or perhaps even less, appears to be a sufficient 
minimum for maintenance. As the supply of nonnitrogenous ma- 
terials is reduced a larger supply of feed protein seems to be required 
to reach equilibrium because more and more of it is diverted for 
use as fuel, so that in the total absence of nonnitrogenous nutrients 
a large excess of protein must be fed before equilibrium between in- 
come and outgo is reached. In interpreting experiments or formulat- 



1 Compare Armsby, Principles of Animal Nutrition, pp. 117-127. 



88 



MAINTENANCE RATIONS OF FARM ANIMALS. 



ing a maintenance ration, therefore, it is not sufficient to consider 
simply the amount of protein, but account must be taken of the 
supply of nonnitrogenous materials. 

VALUE OF NONPROTEIN. 

The crude protein of the feed of farm animals includes not only 
true protein but a great variety of other nitrogenous substances, 
grouped for convenience under the designation " Nonprotein." In 
considering the results of experiments upon the protein require- 
ments of these animals, therefore, it is necessary to determine 
whether the true protein should be the basis of comparison or 
whether the nonprotein has some value for maintaining the protein 
tissues of the body. 

The writer has recently 1 considered in some detail the experimen- 
tal evidence on this point, and the discussion need not be repeated 
here. It appears to have been demonstrated by recent experimental 
results, especially by those of Kellner, Morgen, and the Laboratory 
for Agricultural Research in Copenhagen, that the nonprotein of 
ordinary feeding stuffs is available for the maintenance of rumi- 
nants, probably indirectly through a conversion to protein by means 
of bacteria in the digestive tract. On the other hand, investigations 
have not thus far shown that such nonprotein has any material value 
for production purposes. The writer therefore reached the conclusion 
th|it for the present, pending further investigation, it is desirable to 
consider ordinarily only the digestible true protein in the compu- 
tation of rations for productive purposes, ignoring the nonprotein. 
This implies, however, that a discussion of the results of experi- 
ments upon the protein requirement shall also be based upon the 
amounts of true protein supplied and not upon the crude protein. 
This will have two effects. 

First, it will make the protein requirement appear smaller than it 
realh 7 is. Suppose, for example, that a series of trials in which the 
ratio of digestible nonprotein to digestible protein is 1 : 10 shows 
that nitrogen equilibrium is reached with a ration supplying 500 
grams protein and 50 grams nonprotein. Regarding the true protein 
only, the maintenance requirement is 500 grams, while the real re- 
quirement of the animal is 550 grams. 

In the second place, however, this error will be largely compensated 
for when the actual computation of rations is also based on the true 
protein. Thus in the case just supposed, if a maintenance ration 
be computed from any feed or mixture in which the ratio of non- 
protein to protein is the same as in the experiments from which the 
maintenance requirement was deduced, viz, 1 : 10, it is obvious that 
the same final result will be reached whether the maintenance require- 



1 Bureau of Animal Industry, Bulletin 139. 



PROTEIN REQUIREMENT OF CATTLE. 



89 



ment be considered to be 500 grams of true protein or 550 grams of 
crude protein. Only when the proportion of nonprotein to true pro- 
tein varies widely from that existing in the rations used in determin- 
ing the protein requirement will any significant error arise in comput- 
ing rations. 

In the results considered on succeeding pages, both the crude pro- 
tein and true protein of the rations are stated when these are given 
in the reports of the experiments. 

MINIMUM OF PROTEIN FOR FARM ANIMALS. 

In considering the protein supply of different species of farm 
animals, it is important to distinguish between two points of view. 
On the one hand, it may be sought to determine the least amount 
of protein upon which the protein tissues of the animal can be 
maintained. This might be called the physiological minimum. It 
shows the proportion of protein in a productive ration which is de- 
voted solely to maintenance. On the other hand, the endeavor may 
be to formulate the most advantageous amount of protein to supply 
when an animal is actually to be maintained for a time and this 
amount may very possibly be greater than the physiological mini- 
mum. The first point of view, however, is plainly the fundamental 
one and should receive our first consideration. Having determined 
the lower limit of protein supply, it will then be possible to consider 
intelligently the advantages, if any, of a surplus. 

CATTLE. 

For obvious reasons it is impracticable to ascertain the fasting 
katabolism of ruminants ; their maintenance requirement as regards 
protein must, therefore, be determined by a process of trial. 

Tlie earliest, and for a long time the only, determinations of the maintenance 
requirements of cattle were those of Henneberg and Stohmann in 1S5S, the 
results of which as regards energy were cited on page 39. In 6 experiments 
the minimum amount of digestible crude protein (total nitrogen X 6.25) sup- 
plied per day was 0.35 pound per 1,000 pounds live weight and this quan- 
tity seemed to be more than sufficient for maintenance. On the average of the 
6 experiments, in 2 of which there was some loss of body protein, 0.53 
pound of digestible crude protein was consumed per 1,000 pounds live 
weight. Wolff's standard for maintenance, long current, viz, 0.7 pound di- 
gestible crude protein, was based on Henneberg and Stohmann's experiments 
with an allowance for the fact that their experiments were made at a relatively 
high temperature. Wolff's standard, however, was intended as a guide for 
actual maintenance feeding rather than as an expression of the minimum 
protein requirement. 

In the light of later experience, the methods of these earlier experiments 
must be considered imperfect and their results are now chiefly of historical 
interest. The first experiments by modern methods were those of G. Kiihn and 



90 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Kellner at the Moeckern Experiment Station, 1 which include determinations 
of the gain or loss of fat as well as of protein and hence afford a secure basis 
for judgment as to the sufficiency of the energy supply. Including subsequent 
slight corrections by Kellner, 2 the principal results as regards protein are sum- 
marized in the following table : 



Gain or loss of protein by cattle — G. Kiihn and Kellner. 



No. of animal. 


Live 
weight. 


Protein per day and 1, 
Digestible in feed. 


300 pounds live weight. 
Gain by animal. 


Crude 
protein. 3 


True 
protein. 4 


Protein. 


Fat. 




Pounds. 


Pound. 


Pound. 


Grams. 


Grams. 


II 


1,394 


0.65 


0.58 


-17.2 


+ 75.8 


Ill 


1,393 


.53 


.35 


-24.5 


+ 63.0 


IV 


1,386 


.53 


.34 


-25.9 


+ 20.4 


V 


1,327 


.75 


.60 


+21.8 


+106.6 


VI 


1,420 


.71 


.57 


+11.8 


+ 119.3 


XX 


1,481 


.80 


.65 


- 3.2 


+ 71.7 


A 


1,365 


.71 


.56 


+27.2 


+103.0 


B 


1,348 


.35 


.28 


-65.3 


. - 78.0 



If the very small loss of protein by ox XX may be regarded as falling 
within the limits of experimental error, the eight experiments may be averaged 
as follows : 



Animal. 


Digestible in feed. 


Gain by animal. 


Crude 
protein. 


True 
protein. 


Protein. 


Fat. 


Animals V, VI, XX, and A 

Animal II 


Pound. 
0.74 
.65 
.47 


Pound. 
0. 60 
.58 
.32 


Grams. 
14.4 
-17.2 
-38.6 


Grams. 
+ 100.2 
+ 75.8 
+ 5.4 


Animals III, IV, and B 



It appears that approximately 0.6 pound of digestible true protein or 0.74 
pound of crude protein per 1,000 pounds live weight was at least sufficient to 
rather more than maintain nitrogen equilibrium when the total energy supply 
in the ration was sufficient to cause a small gain of fat, while half this amount 
of true protein or 0.47 pound of crude protein was manifestly insufficient. A 
reduction to 0.35 pound digestible true protein or 0.53 pound digestible crude 
protein in the cases of ox III and ox IV, even with a sufficient supply of non- 
nitrogenous material to cause some gain of fat, resulted in a loss of protein 
from the body, while in the case of ox B, with a slightly lower supply of true 
protein and a materially lower one of crude protein and a ration materially 
below the maintenance requirement, the loss of protein was still greater. The 
considerable loss of protein by ox II is not readily explicable. 

Experiments upon the same subject were also made by the writer 5 in 1892- 
1898, ehiefty upon rations of timothy or mixed hay, with the addition in Ex- 
periment VII of starch, but also, in Experiment VIII, upon a ration consisting 

1 Die Landwirtschaftlichen Versuchs-Stationen, vol. 44, p. 257 ; vol. 47, p. 275. 

2 Die Ernahrung der Landwirtschaftliche Nutztiere, 5th ed., p. 411. 

3 Corrected for estimated loss of nitrogen in drying of feces. 

4 As reported in the original account of these experiments. 

5 Pennsylvania Experiment Station, Bulletin 42, p. 165. 



PROTEIN REQUIREMENT OF CATTLE. 



91 



chiefly of grain together with a minhnuni of wheat straw. The results of these 
experiments are contained in the following table : 



Nitrogen balance per 1.000 pounds live weight — Armsby. 





Digestible in feed. 


Nutritive 
ratio 1: 


Odin or loss 


Jkxperinieni . 


Crude 
protein. 


True 
protein. 


of nitrogen. 
t)v 1)0 dv. 


Experiment I: 

Steer 1 


Pound. 
0.30 


Pound. 
0.26 


20.1 


Grams. 


Steer 2 


. 27 


23 


20. 4 


— . 4 




!31 


. 27 


18. 6 


— 1. 2 


Experiment II: 

Steer 1 


.45 


.38 


13.4 


+1.9 


Steer 2 


.47 


.40 


13.6 


+ 4.2 




.49 


.42 


12.8 


+5.2 


Experiment VI: 

Steer 1 


.62 


.59 


10.9 


+4.7 




.60 


.55 


10.9 


+6.0 




.67 
.49 


.63 


10.6 


+2.8 


Experiment VII: 

Steer 1 


.31 


23.0 


+5.7 


Steer 2 


.44 


.26 


25.3 


+3.7 


Steer 3 


.51 


.30 


23.9 


+4.4 


Experiment VIII: 

Steer 1 


.62 


.52 


10.4 


+ .2 




.57 


.48 


10.7 


- .1 




.66 


.55 


10.6 


-2.0 













In Experiments II, VI, VII, and VIII digestible crude protein ranging from 
0.44 to 0.67 pound fully sufficed for maintenance, with a single exception. The 
range of true protein was somewhat wider, viz, 0.26 to 0.63 pound. The rations 
of Experiment VII were relatively richer in nonprotein than were those of the 
other experiments, and the adequacy of these very low protein rations sug- 
gests a utilization of the nonprotein, although the abundance of nonnitrogenous 
nutrients, as shown by the nutritive ratio, may also be a factor. The rations 
of Experiment I were obviously inadequate, even although the supply of non- 
nitrogenous matter was liberal. 

Experiments upon a steer by xVrmsby and Fries 1 in which the respiratory 
products were determined gave results in general accord with those already 
cited. Computed per 1,000 pounds live weight, these results were as follows : 



Witroffen balance per 1,000 pounds live weight — Annbsy and Fries. 





Digestible. 


Gain or loss by body. 


Crude 
protein. 


True 
protein. 


Nitrogen. 


Fat. 




1902. 


Pound. 


Pound. 


Grams. 


Grams. 


Period A 




0.45 


0.36 


- 9.1 


-286. 5 


Period B 




.52 


.42 


- 1.3 


- 89.2 


Period C 




.53 


.44 


- .4 


+ .6 


Period D 




.68 


.55 


+12.3 


+ 16.8 




1903. 










Period I 




.66 


.46 


-16.4 


-192.9 


Period II 




.51 


.38 


-15.0 


-350. 8 


Period III 




.70 


.53 


- 2.3 


-169.7 


Period TV 




.97 


.84 


+ 9.2 


+196. 4 




1904. 














.44 


.34 


- 9.5 


-312.7 


Period 11 




.74 


.55 


- .8 


- 75.2 


Period III 




.60 


.46 


- .5 


-155.4 







1 Bureau of Animal Industry, Bulletins 51, 74, and 101. 



92 



MAINTENANCE RATIONS OF FARM ANIMALS. 



In periods C and D of 1902 and period IV of 1903, the only ones in which 
maintenance was reached, the crude protein ranged from 0.53 to 0.97 and the 
true protein from 0.44 to 0.84. In a later series of experiments 1 on two 
immature steers, from 0.92 to 1.13 pounds of crude protein, or 0.69 to 0.77 
pound true protein per 1,000 pounds live weight sufficed for maintenance in 
three periods in which there was some gain of fat. The experiments furnished 
no evidence that so large an amount was necessary, since the next lowest 
amount was 0.44 pound crude protein or 0.37 pound true protein in a ration 
producing a slight gain of fat but a small loss of protein. 

The investigations of the Laboratory for Agricultural Research in Copen- 
hagen upon the protein requirements for milk production include also two ex- 
periments on dry cows 2 with rations furnishing relatively small amounts of 
digestible nitrogenous matter, chiefly in the form of true protein. The periods 
in which an approximate nitrogen balance was secured gave the following data : 



Nitrogen balance of dry cows per day and head — Copenhagen experiments. 



Cow and period. 


Live 
weight. 


Crude protein 
(N. X 6.25) digested. 


Gain of 
nitrogen 
per head 
by animal. 


Per head. 


Per 1,000 
pounds 
live weight. 


Cow 117: 

Period 2 .- 


488 
485 

466 
443 


Grams. 
87.5 
100.0 

143.8 
112.5 


Pound. 
0. 18 
.21 

.31 
.25 


Grams. 

-3 
+2 

-5 
+3 


Period 4 


Cow 134: 

Period 1 


Period 4 





The experiments on milking cows also afford approximate data as to the main- 
tenance requirement. If the protein of the milk is subtracted from the total 
digestible protein of the feed, the remainder is obviously the maximum amount 
which was available for maintenance. In Bulletin 139 of this bureau, 
pages 38-39, there are given the results of those experiments in which the 
smallest amounts of protein were consumed. Selecting from among these those 
in which there was an approximate nitrogen equilibrium, we obtain the results 
tabulated below : 



Daily gain or loss of protein by cows — Copenhagen experiments. 



Cow and period. 


Live 
weight. 


Crude 
protein 
digested. 


Protein 
of milk. 


Maximum 
crude pro- 
tein avail- 
able for 
mainten- 
ance. 


Gain of 
protein by 
animal. 


Sixtieth report: 


Kilos. 


Grams. 


Grams. 


Grams. 


Grams. 


Cow No. 10, period 6 


446 


600.0 


387. 5 


212.5 


-12.5 


Cow No. 53, period 4 


454 


543.8 


350.0 


193.8 


-12.5 


Cow No. 53, period 6 


451 


568.8 


306.3 


262.5 


+18.8 


Cow No. 68, period 4 


461 


575.0 


393.8 


181.2 


-31.3 


Cow No. 68, period 14 


441 


506.3 


312.5 


193.8 


-12.5 


Cow No. 58, period 4 


485 


531.3 


325. 


206.3 


- 6.3 


Cow No. 58, period 6 


485 


581.3 


293.8 


287.5 


+37.5 


Sixty-third report: 












Cow No. 68, period 6 


453 


575.0 


368.7 


206.3 


-25.0 



1 Bureau of Animal Industry, Bulletin 128. 

2 Sixty-third Report, pp. 28 and 30. 



PROTEIN REQUIREMENT OF CATTLE. 93 

In tne two periods in which there was a gain of protein by the animal the 
crude protein available for maintenance, computed per 1,000 pounds live weight, 
was: Pound. 

Cow No. 53, period 6 0. 58 

Cow No. 58, period 6 . 59 

In the four periods in which the loss of protein by the animal did not exceed 
12.5 grams (2 grams nitrogen) the corresponding amounts were: 

Pound. 

Cow No. 10, period 6 0. 48 

Cow No. 53, period 4 . 43 

Cow No. 68, period 14 .44 

Cow No. 58, period 4 . 43 

These results are quite of the same order as those obtained by Kellner and by 



Armsby, while those on the two dry cows are much lower, with the exception of 
a single result of Armsby's. (Experiment I, steer 2.) 

In drawing conclusions from the results recorded in the foregoing 
pages, it is important to remember that what it is sought to determine 
is the minimum protein requirement. As has been shown on previous 
pages, an excess of feed protein above this minimum is, in the case of 
the mature animal, substantially all katabolized, producing no mate- 
rial gain of protein. The fact of an equality of income and outgo 
of nitrogen upon a given ration of protein, therefore, while it shows 
that the quantity consumed is sufficient for maintenance does not 
show that a smaller amount would not suffice. What we have to 
consider is the evidence of the experiments regarding the least 
amount sufficient for maintenance. It is evident that this minimum 
amount is relatively small, but it is also evident that the recorded 
results do not suffice to fix with certainty the absolute minimum. 

The lowest recorded amounts per 1,000 pounds live weight upon 
which nitrogen equilibrium was reached were 0.21 pound and 0.25 
pound of crude protein in the Copenhagen experiments on dry cows, 
while almost as small a quantity, viz, 0.27 pound crude protein or 0.23 
pound true protein in Armsby's Experiment I, steer 2, fell very 
little short of reaching nitrogen equilibrium. Aside from these 
somewhat exceptional results, the lowest figures obtained per 1,000 
pounds live weight were 0.43 pound crude protein and 0.38 pound 
true protein, The maximum is found in Armsby and Fries' experi- 
ment of 1903-4, viz, 0.96 pound crude protein and 0.84 pound true 
protein, but it seems altogether probable that the animal in this 
period was consuming a surplus of protein. If we omit these few 
extreme results in either direction, the average and range of the 
results of the other experiments are as follows : 



Average and range of protein requirements of cattle. 





Number of 


Protein requirement. 




experi- 




Maximum. 






ments. 


Average. 


Minimum. 






Pound. 


Pound. 


Pound. 


Crude protein 


19 


0. 55 


0. 75 


0.43 


True protein 


12 


. 52 


.63 


.38 



94 



MAINTENANCE RATIONS OF FARM ANIMALS. 



It seems safe, therefore, to estimate 0.6 pound of crude protein or 0.5 
pound true protein per 1,000 pounds live weight as representing in a 
general wa} T the minimum protein requirement of mature cattle with a 
probable range of 0.1 or 0.2 pound either way under varying conditions. 

For actual maintenance feeding it is probable that a somewhat 
more liberal supply of protein than is indicated by these figures 
would be advisable. Rations so poor in protein, if containing an 
adequate amount of nonnitrogenous matter, would probably suffer a 
loss through failure of the animal fully to digest the nonnitrogenous 
matter. A somewhat narrower nutritive ratio could readily be 
reached in practice in ordinary feeding without additional expense 
and from the standpoint of digestibility would very likely be justified. 

SHEEP. 

While a considerable number of experiments with sheep are on 
record in which approximate maintenance as a whole was observed, 
at least so far as could be judged from the live weight, few of them 
afford satisfactory data as to the minimum protein requirement. 
For the immediate purpose of this discussion, only experiments in 
which the nitrogen balance was actually determined are available, 
mere maintenance of weight being too uncertain a criterion. 

A distinct difference between cattle and sheep, which affects the protein 
requirement, lies in the greater demand for protein incident to the growth of 
wool in the latter animals as compared with that of hair in the former. The 
results of determinations by Armsby and Fries 1 on the same two steers in two 
consecutive winters showed an average production of epidermal tissue, includ- 
ing the growth of hair and the loss in brushings, equivalent to 0.19 gram nitro- 
gen per day and 1.000 pounds live weight, which is equal to 0.0025 pound pro- 
tein, an amount too small to materially affect our estimates of the maintenance 
requirement. In the case of sheep, determinations of the growth of wool by 
several investigators afford the following data regarding the average amount 
of protein required for this purpose. The results have been computed per 
1.000 pounds live weight for the sake of ready comparison : 

Protein contained in daily growth of toool per 1,000 pounds live weight. 

Pound. 

Henneberg, Kern, and Wattenberg 2 Mature sheep 0.132 

Henneberg, Kern, and Wattenberg 3 Lambs .143 

Weiske 4 Growing sheep .100 

Henneberg and Pfeiffer 5 Mature sheep . 149 

Pfeiffer and Kalb 6 Mature sheep . 150 

Average . 135 

Although, as the foregoing figures show, the protein requirements of sheep 
for the growth of wool are considerably greater than those of cattle for the 

1 Bureau of Animal Industry, Bulletin 128. 
- Journal fur Landwirtschaft, vol. 26, p. 549. 
8 Ibid., vol. 28, p. 289. 

4 Landwirtschaftliche Jahrbiicher, vol. 9, p. 205. 

5 Journal fur Landwirtschaft, vol. 38, p. 215. 

6 Landwirtschaftliche Jahrbiicher, vol. 23, p. 175. 



PROTEIN REQUIREMENT OF SHEEP. 



95 



growth of hair, the absolute difference, after all, does not add very greatly to 
the total maintenance requirement. 

In Henneberg and Stohmann's Weende experiments 1 upon two sheep fed 
exclusively on meadow hay, there was digested on the average per 1,000 pounds 



live weight: Pounds. 

Crude protein (total N X 6.25) 1.32 2 

Nitrogen-free extract 6. 28 

Crude fiber 3.93 

Ether extract . 32 



and the animal gained 0.17 pound of body protein, in addition to that stored 
in the wool, and a small amount of body fat. 

In a series of 20 digestion and metabolism experiments by Schulze and 
Marcker, 3 decidedly smaller amounts of protein proved sufficient to maintain 
nitrogen equilibrium. In one case on a ration containing as little as 0.335 
pound digestible crude protein per 1,000 pounds live weight, but having a very 
wide nutritive ratio (1: 17.2) there was a slight gain of total protein, but one 
less than the amount required for the growth of wool. If we exclude this 
experiment and also 4 experiments in which it is evident that an excess of 
protein was fed, we have as the average of 6 experiments in which no loss of 
body protein was observed 0.653 pound digestible crude protein per 1,000 
pounds live weight, while in two other experiments in which the minimum 
losses of 0.005 and 0.015 pound body protein were observed, the protein supply 
was, respectively, 0.655 and 0.690 pound. It is evident, then, that the protein 
supply of the sheep can be materially reduced below the amount fed in Henne- 
berg and Stohmann's experiments without leading to a loss of body protein. 

That such is the case seems to be clearly shown by the recent investigations 
of Katayama at the Moeckern Experiment Station, 4 in which increasing amounts 
of nearly pure protein (" aleuronat ") were added to a basal ration very poor 
in protein, consisting of hay, oat straw, starch, and cane sugar. The protein in 
every case was substituted for a corresponding amount of starch, so that the 
total energy of the ration remained substantially unchanged. In the third 
period of the experiment both of the two sheep showed some loss of body pro- 
tein, while in the fourth period, with more protein in the food, a gain was noted. 
In neither case was the growth of wool taken into consideration. By adding in 
the one case the loss of body protein to the digestible protein of the food and 
in the other period subtracting the gain, the author gets the following comparison : 



Protein requirement of sheep per day and head — Katayama. 





Sheep I 
(weight, 34 
kilograms). 


Sheep II 
(weight, 38 
kilograms). 


Period III: 

Nitrogen digested 


Grams. 
1. 978 
.079 


Grams. 
2. 412 
.216 


Loss of body protein 


Period IV: 

Nitrogen digested 


2. 057 


2.628 


3. 176 
1. 107 


3.360 
.515 


Gain of body nitrogen 


Average for maintenance 


2. 069 


2. 845 


2. 063 


2. 737 


Maintenance per 1,000 pounds live weight: 

Nitrogen 


.061 
.379 


.072 
.450 


Protein 





1 Neue Beitrage, etc. 

2 Estimated by Kellner to contain 1.04 pounds of true protein. 

3 Wolff : Die Ernahrung der Landwirtschaftlichen Nutztiere, p. 300. 
* Die Landwirtschaftlichen Versuch-Stationen, vol. 69, p. 321. 



96 



MAINTENANCE RATIONS OF FARM ANIMALS. 



On the average of the two animals, 0.41 pound digestible crude protein per 
1,000 pounds live weight was apparently sufficient to prevent a loss of nitrogen 
from the body. The crude protein in this case was practically all true protein, 
only minimum amounts of nonprotein being present in the ration. Since, how- 
ever, the growth of wool must have gone on, with a corresponding storage of 
nitrogen, this apparent maintenance ration would really result in a loss of 
protein by the active tissues of the body. 

If we add to Katayama's average 0.14 pound per 1,000 pounds 
live weight for the growth of wool, we get 0.55 pound as represent- 
ing the minimum protein requirement for the maintenance of mature 
sheep, including the growth of wool. It is interesting to note that, 
according to these figures, the actual maintenance requirement for 
the body tissues is quite as low relatively as for cattle. 

It is true that some earlier experiments seem to indicate a greater 
demand for protein than the foregoing figures show. Thus, in 
the experiments cited on page 80 to illustrate the influence of the 
protein supply upon its katabolism, a ration containing about 2.5 
pounds digestible protein per 1,000 pounds live weight seemed to be 
about sufficient for maintenance, including the wool production, 
while a ration containing 2.27 pounds showed a loss of protein. Simi- 
larly, in earlier experiments b}^ Henneberg, Fleischer, and Miiller, 1 
a ration containing 1.25 pounds digestible crude protein following 
one supplying 6.51 pounds resulted in a loss of protein by the animal. 
Notwithstanding these isolated results, however, it seems justifiable 
to accept the lower figure obtained by Katayama as representing ap- 
proximately the minimum protein requirement of mature sheep. 

SWINE. 

The only data available as to the minimum protein requirement of 
swine are derived from the two experiments upon fasting animals by 
Meissl, Strohmer, and Lorenz (referred to on p. 51). The animals 
were Yorkshire swine, one 14 months old and weighing 140 kilograms, 
and the second, whose age is not given, weighing 120 kilograms. In 
the fasting state the nitrogen excretion of these animals was as 
follows : 





Live 
weight. 


Nitrogen 
excretion. 


Animal I: 
Animal II: 

Average of third, fourth, and fifth days' fasting 


Kilos. 
140 

120 


Grams. 
9.80 

a. 7, 



The nitrogen excretion was equivalent, respectively, to 0.44 and 
0.35 pound of protein per 1,000 pounds live weight, or about the 
amounts which appear to be required for cattle and sheep. No 

1 Jahresbericht der Agricnlturchemie, vols. 16-17, II, p. 145. 



THE OPTIMUM OF PROTEIN. 



97 



experiments are on record which demonstrate the sufficiency of this 
amount as a maintenance ration. 

the: horse. 

In the experiments by Grandeau and Le Clerc described on pages 
62-63 the nitrogen balance of the horses was determined during 6 of 
the periods. The following table shows the amounts of protein and 
of nonprotein nitrogen digested in each period, the urinary nitrogen, 
and the small losses in epithelial tissue (epidermis, hoofs, hair, etc.) : 



Nitrogen balance of horses — Grandeau and Le Clerc. 





Horse No. 1. 


Horse No. 2. 


Horse No. 3. 


January, 
1884. 


April, 1884. 


November, 
1883. 


May, 1884. 


December, 
1883. 


March, 
1884. 


Digested: 

Protein nitrogen 

Nonprotein nitrogen 

Total nitrogen 

Nitrogen of epithelial tissue . . . 

Urinary nitrogen 

Nitrogen gained 


Grams. 
43. 19 
1.20 


Grams. 
34.29 
- 1.01 


Grams. 
38.94 
- 3.23 


Grams. 
34.22 
10. 78 


Grams. 
41.82 
- 2.09 


Grams. 
24. 72 
- 4.58 


44. 39 


33. 28 


35.71 


35.00 


39. 73 


20.14 


1.46 
35.17 
7.76 


1.46 
38.75 
- 6.93 


1.46 
30.70 
3.55 


1.46 
41.92 
1.62 


1.46 
37.62 
.65 


1.46 
32.70 
-14.02 



Omitting the results upon horse No. 3 in March, when the diges- 
tible protein was exceptionally low, the other five periods show an 
average daily gain of nitrogen of 1.33 grams, while the average crude 
protein digested (total N.X^.25) was 235 grams, equivalent to 0.59 
pound per 1,000 pounds live weight. 



THE OPTIMUM OF PROTEIN. 

The data of the foregoing paragraphs seem to indicate a striking 
uniformity in the minimum protein requirement of the principal spe- 
cies of domestic animals when mature, 0.4 to 0.6 pound per 1,000 
pounds live weight apparently sufficing to maintain nitrogen equilib- 
rium under favorable conditions. 

It should be clearly understood, however, that this figure repre- 
sents a more or less accurately determined limit. It purports to be 
the amount below which the protein supply can not be reduced 
without eventual protein starvation. The animal body, however, 
may adjust itself to a wide range of protein supply above the mini- 
mum, using some of it to increase the stock of protein in the body 
and katabolizing the remainder as fuel material. An increase in the 
protein supply above the minimum results, after a relatively short 
time, in the maintenance of the body protein at a higher level. The 
practical question in actual maintenance is far less in regard to the 
8489°— Bull. 143—12 7 



98 



MAINTENANCE RATIONS OF FARM ANIMALS. 



least amount of protein which may be used than as to the most ad- 
vantageous level of protein nutrition; that is, as to the optimum of 
protein. 

This question has been warmly debated in connection with human 
nutrition. 

Numerous recent investigations, notably those by Chittenden and his asso- 
ciates, 1 have shown that the protein of human dietaries can be reduced much 
below the amount previously regarded as necessary. In most cases there is no 
possibility of a direct comparison with the fasting katabolism of the same indi- 
vidual, but as previously stated (p. 77) a considerable number of instances are 
on record in which the nitrogen supply has been reduced to an amount mate- 
rially lower than that usually found for the fasting protein katabolism of 
individuals of the same weight without leading to a loss of protein from the 
body. In all these experiments, the nonnitrogenous nutrients consisted, as is 
usually the case in human dietaries, to a considerable extent of carbohydrates. 

Moreover, while some of the earlier experiments were for short periods and 
on comparatively few individuals, Chittenden's investigations covered long 
periods and were made on 26 different individuals, including 5 professional men 
under observation for 8 months, 13 soldiers observed for 6 months, 
and 8 trained athletes under observation for 5 months. His results clearly 
demonstrate the possibility of maintaining the body protein and fully preserv- 
ing the health and vigor upon a low protein diet. In other words, a relatively 
low level of protein nutrition for several months is not inconsistent with health 
and efficiency. 

In some of the earlier experiments in which very low protein diets were fed 
to dogs, the health of the animals suffered seriously and there has been a 
tendency to ascribe these ill effects to the continued use of very small amounts 
of protein. Later investigations by Chittenden, however, in which dogs were 
kept on a low protein diet for the greater part of a year, seem to have demon- 
strated that the ill effects observed in the earlier experiments were due to un- 
hygienic conditions and not to the low protein diet. It may be remarked that in 
experiments upon cattle, rations very low in protein have been fed for a con- 
siderable time without any perceptible deleterious effects. No similar determi- 
nations upon other species of farm animals appear to have been made. 

On the whole, then, it can not be said that a considerable surplus of 
protein over the minimum requirement for maintenance — that is, the 
maintenance of protein nutrition on a high plane — has been proved 
to be of any material advantage in the maintenance either of men or 
domestic animals during periods covering several months. Whether 
a continued low protein diet through years or generations would 
show a different result is at present largely a matter of speculation. 
It is to be remarked, however, that the particular point under dis- 
cussion is the protein requirement of the mature organism. That a 
deficiency of protein in the diet of a growing animal may have 
disastrous results is clear. If, however, the habitual food supply 
of a race of men or a group of animals is low in protein, the young 
are likely to share this deficiency with the mature, and it seems not 



1 Physiological Economy in Nutrition. Stokes Co., 1907. 



RELATIVE VALUES OF PROTEINS. 



99 



impossible that this is an important factor in the alleged physical 
inferiority of certain races of men living on a low protein diet. 
This consideration warns us to exercise care in this respect in the 
management of the breeding herd. 

In the actual maintenance feeding of farm animals, the matter of 
the digestibility of the ration must also be considered. It has been 
shown that a relative deficiency of protein in the ration tends to 
depress the apparent digestibility of both the protein and nonnitro- 
'genous nutrients, especially in the case of ruminants. A maintenance 
ration for these animals containing the minimum amount of protein, 
together with the quantities of nonnitrogenous nutrients required to 
maintain the energy supply, would have a nutritive ratio, computed 
in the ordinary way, of approximately 1 : 12. On such a ration, there 
would, in all probability, be some loss of digestibility. An increase 
of its protein by 50 per cent would very probably effect a gain in 
digestibility which would more than offset the increased cost, if any. 
Indeed, unless feeds especially poor in protein are used, it may often 
be difficult, even if desirable, to reduce the protein content of a main- 
tenance ration to the low level of absolute necessity. 

RELATIVE VALUES OF PROTEINS. 

In the discussions of the foregoing paragraphs, following the usual 
practice, the word protein has been used as if it designated a single 
chemical individual. In reality, of course, this is very far from 
being the case. The protein of the body or of the feed in this con- 
ventional sense includes a large number of distinct and in some re- 
spects, widely differing proteins. The studies of the chemical struc- 
ture of the protein molecule made in recent years, beginning with the 
fundamental investigations of Emil Fischer, have shown marked dif- 
ferences in the proportions of the various "building stones" (amino- 
acids, etc.) contained in different proteins, while studies in immunity 
have led to the recognition of marked specific and individual bio- 
logical differences in animal proteins, although these have not been 
definitely correlated with differences of chemical constitution. It is 
pertinent to inquire, therefore, whether we are justified in discussing 
the nutritive functions of feed protein as a group or whether we must 
consider each individual protein by itself. In other words, are there 
recognizable differences in nutritive value between individual pro- 
teins ? 

DIFFERENCES IN CONSTITUTION OF PROTEINS. 

In discussions of this question, the chief emphasis has been laid 
upon the demonstrated differences in the proportions of the various 
cleavage products yielded by the different proteins when subjected 



100 



MAINTENANCE RATIONS OF FARM ANIMALS. 



to acid hydrolysis. The following table shows some of the more 
recent results obtained by Abderhalden and by Osborne : 



Constituents of proteins — Abderhalden and Osborne. 



Constituents. 


Gliadin 

of 
wheat. 1 


Gluten- 
in of 

wheat. 1 


Zein 
of 
maize. 1 


Pha- 
seolin of 
white 
bean. 1 


Casein. 2 


Egg 
albu- 
min. 2 


Serum 
albu- 
min of 
horse 
blood. 2 


Serum 
globu- 
lin of 
horse 
blood. 2 


Ox 
mus- 
cle. 3 


Edestin 

from 
hemp. 4 


Glycocol 


P. ct. 


P. ct. 
0.89 
4. 65 

.24 
5. 95 
M. 23 
1.97 

.91 
23.42 

.74 
4.25 

.02 
1.92 
1.76 
4.72 
4.01 
( 5 ) 


P. ct. 


P. ct. 
0.55 
1.80 

1.04 
9. 56 
2.77 
3.25 
5.24 
14.54 
.38 
2.17 


P. ct. 
0.00 
. 90 

1.00 
10. 50 
3.10 
3.20 
1.20 
11.00 
.23 
4.50 
.06 
5.80 
2.59 
4.84 
1.95 
1.50 


P. ct. 
0.00 
2. 10 


P. ct. 
0.0 
2. 7 


P. ct. 
3.5 
2. 2 

( 5 ) 
18. 7 
1 2.8 
3.8 
2.5 
8.5 


P. Ct. 

2.06 
3. 72 

.81 

11.65 
5.82 
3.15 
4.51 

15.49 
(?) 
2.20 


P. ct. 
3.80 
3. 60 

( 5 ) 

20. 90 

8 1.70 
2.40 
4.50 

7 6.30 
.33 
2.10 
.25 
1.00 
1.10 

11.70 


Alanin 


2.00 

.21 
5. 61 
7.06 
2.35 
.58 
37.33 
.13 
1.20 
.45 
.00 
.61 
3.16 
5.11 
( 8 ) 




Amino- valerianic 
acid 








6. 10 
2.25 
4.40 
1.50 
9.10 


20. 
i 1.0 
3.1 
3.1 
7.7 
.6 
2.1 
2.3 


Prolin 




Phenylalanin 




Aspartic acid 

Glutamic acid 

Serin 


"ih'.hi 


Tyrosin 




1.10 
.20 


2.5 
.7 


Cystin 




Lysin 


.00 
.81 
- 1.82 
3.61 
.00 


3.59 
1.97 
4.72 
2.06 

( 5 ) 


7.59 
1.76 
7.47 
1.07 

( 5 ) 


Histidin 








Arginin 








Ammonia 


1.63 






Tryptophan 

Total 


( 5 ) 


( 5 ) 


( 5 ) 


65.81 


59.66 


23.11 


53.64 


52.37 


28. 38 


42.6 


45.2 


67.30 









1 Osborne. The proteins of the wheat kernel, pp. 110, 113, and 118. 

2 Abderhalden. Lehrbuch der physiologischen Chemie. 

3 Osborne. The American Journal of Physiology, vol. 24, p. 437. 

4 Abderhalden. Loc. cit. 

5 Present. 

6 A prolin. 

7 A later determination by Osborne (American Journal of Physiology, vol. 15, p. 333), 
confirmed by Abderhalden, gave 18.74 per cent. 



While many of the figures of the foregoing table can not lay claim to a high 
degree of quantitative accuracy, it is, nevertheless, clear that the proportions 
of the various atomic groupings in the protein molecule vary within wide 
limits, while in some cases the most careful search has failed to show the 
presence of certain constituents. Thus, glycocol and lysin were not found in 
gliadin, nor lysin and tryptophan in zein, while ox muscle yielded a consider- 
able percentage of lysin, a moderate amount of glycocol, and showed the pres- 
ence of tryptophan. 



ABSENCE OF CERTAIN CONSTITUENTS. 



There is now a general agreement that in the process of digestion the pro- 
teins of the feed undergo extensive cleavage and are to a large extent broken 
down either into individual amino-acids or into comparatively simple peptid- 
like compounds. These substances are resorbed by the intestinal epithelium 
and the diverse proteins of the body are formed from them by synthetic proc- 
esses, either in the intestinal wall or beyond. Such being the case, it has 
seemed clear that, for example, the proteins of ox muscle containing 2.06 per 
cent of glycocol and 7.59 per cent lysin could not be produced from gliadin. 
which is lacking in both these groups, nor from zein, which lacks lysin and 
tryptophan. 

The classic example of the effects of such a deficiency is, of course, gelatin, 
which contains neither tyrosin, cystin, nor tryptophan. Bischoff and Voit 1 



1 Hermann's Ilandbuch dor Physiologie, vol. 6, pp. 122 and 395. 



RELATIVE VALUES OE PROTEINS. 



101 



long ago showed that gelatin in whatever amount fed is completely katabolized 
in the body, at least so far as its nitrogen is concerned, although it may some- 
what diminish the waste of protein tissue. Subsequent investigations by Kirch- 
mann 1 and by Krummacher 2 showed that when gelatin is fed alone an amount 
equivalent to the fasting nitrogen katabolism may reduce the loss of nitrogen 
from the body by something over 20 per cent, while, on the other hand, even 
very large quantities can effect a reduction of only about 35 per cent. Murlin 8 
finds that in the mixed diet of men about two-thirds of the protein may be 
replaced by gelatin without disturbing existing nitrogen equilibrium. That the 
inferior value of gelatin is due to the absence of certain groupings in its mole- 
cule seems to have been shown by Kaufmann, 4 who found that gelatin with the 
addition of proper quantities of tyrosin, cystin, and tryptophan was able to 
maintain nitrogen equilibrium at least several days. 

Investigations by Wilcock and Hopkins 5 upon zein, which, as already noted, 
lacks lysin and tryptophan, approach the subject from a slightly different angle. 
They found that a diet containing zein as its only protein material was unable 
to maintain growth in young mice. The addition of tryptophan approximately 
doubled the survival period and added markedly to the well-being of the ani- 
mals, but was unable to maintain life indefinitely. On the zein diet the animals 
became torpid early in the experiment and almost comatose before death en- 
sued, while with the addition of tryptophan no such symptoms were observed. 
The authors interpret this result as showing that tryptophan has some specific 
function in the body aside from the mere maintenance of nitrogen equilibrium. 
The results recently obtained by Osborne and Mendel, 6 however, show that 
great caution is necessary in the interpretation of such survival experiments, 
while they also indicate that growth is largely dependent on some other factor 
than the protein supply. 

Experiments on rats by Henriques 7 gave a similar result as regards zein, 
with which it was found impossible to obtain nitrogen equilibrium in short 
experiments. On the other hand, however, an abundant supply of gliadin main- 
tained nitrogen equilibrium for some days, notwithstanding the fact that it 
lacks both lysin and glycocol. 

PROPORTIONS OF CONSTITUENTS. 

Still further, even when all the constituents of the body protein are present 
in the feed protein, their proportions may be widely different. Thus, a mixture 
of equal parts of glutenin and gliadin would contain about 30 per cent of glu- 
tamic acid as compared with about half that amount in ox muscle, while the 
latter yields over 11.5 per cent of leucin as compared with less than 6 per cent 
from the former. In such a case it would seem that the tissues in which the 
synthesis takes place must make a selection from the material supplied by the 
digestive tract, reproportioning the various constituents, while the excess of cer- 
tain ones would be attacked by the deamidizing enzyms of the body, their nitro- 
gen being finally excreted as urea. Accordingly, it might be anticipated that the 
more nearly the feed protein resembled in its make-up the average of the body 

1 Zeitschrift fur Biologie, vol. 40, p. 54. 
2 Zeitschrift fur Biologie, vol. 42, p. 242. 

3 American Journal of Physiology, vol. 19, p. 285; vol. 20, p. 234. 

4 Archiv fur die Gesammte Physiologie des Menschen und der Thiere (Pfluger), vol. 109, 
p. 440. 

5 Journal of Physiology (London), vol. 35, p. 88. 

Carnegie Institute of Washington Publication No. 156. 

7 Zeitschrift fur Physiologische Chemie, vol. 60, p. 105. 



102 



MAINTENANCE RATIONS OF FARM ANIMALS. 



proteins the more economically it could be utilized for the building up or repair 
of protein tissues, and that thus there might be very considerable differences in, 
nutritive value between different proteins. 

EXPERIMENTAL METHODS. 

Considerations like the foregoing have been advanced by numerous authors, 
but as yet little satisfactory experimental work upon the relative values of the 
proteins has been reported. Indeed the problem is far from being an easy one. 
Aside from technical difficulties, it is, of course, a simple matter to substitute 
one protein for another in the ration; the difficulty lies in finding a satis- 
factory measure of the effects. The most obvious thing, of course, is a deter- 
mination of the balance of income and outgo of nitrogen, which, when extended 
over reasonably long periods, affords an approximate measure of the relative 
gain or loss of protein. As has been clearly shown on preceding pages, however, 
the nitrogen balance, especially in a mature animal, is a more or less fluctuat- 
ing thing, being materially affected by various factors besides the momentary 
protein supply. Especially important are the influence of the previous pro- 
tein supply upon the general level of protein nutrition, the influence of the 
store of body fat carried by the animal, and the supply of available energy 
in the feed. Only after these influences have been eliminated as completely 
as possible can differences in the nitrogen balance be ascribed to differences 
in the nature of the proteins consumed. On this account, experiments in which 
additions of protein are made to a ration already containing a considerable 
supply and in which gains of nitrogen in different periods are made the basis 
of comparison are quite unsatisfactory, as Magnus-Levy 1 has pointed out. 
A more satisfactory basis of comparison is the amounts of the different pro- 
teins required to maintain nitrogen equilibrium under conditions otherwise 
comparable. Furthermore, the protein supply must not be too liberal. Protein 
supplied in excess of the minimum requirement is utilized largely as fuel ma- 
terial. Under such circumstances, it is easily conceivable that proteins differ- 
ing widely in constitution may furnish enough of each of the essential cleavage 
products to meet the relatively small demand for the maintenance of tissue and 
that thus differences really existing may be masked by the excess of protein 
supplied. 

These considerations clearly indicate that the most promising method of 
investigation is to compare the minimum amounts of the different proteins 
required, along with an abundance of nonnitrogenous nutrients, to maintain 
nitrogen equilibrium on as low a plane of protein nutrition as practicable in 
the same animal in like bodily states and under identical conditions, so far 
as it is possible to insure these. Any consistent differences appearing in a 
considerable number of trials may then, it would seem, be safely ascribed to 
differences in the nature of the proteins. 

Thus far but three investigations, according to the general method just out- 
lined, have been published, all of them appearing within the year 1909. For 
the present purpose it seems superfluous to review the older investigations, 
made by less satisfactory methods and in many cases from a different point 
of view. 

MICHAUD'S INVESTIGATIONS. 

Michaud 2 experimented on three dogs by substantially the method just out- 
lined. Reasoning that any loss in transforming feed protein into body protein 

1 Von Noorden's Handbuch dor Pathologie des Stoffwcchsels, vol. 1, p. 78. 

2 Zeitschrift fur Physiologischo Chemie, vol. 59, p. 405. 



RELATIVE VALUES OF PROTEINS. 



103 



would be smaller the less the difference in the constitution of the two, he used 
as his standard protein supply either dog flesh or the ground flesh and internal 
organs (heart, liver, spleen, and testicles) of dogs. This material may be 
assumed to have supplied the various amino acids, etc., in approximately the 
proportions required to maintain the protein tissues of the experimental animals 
with a minimum of loss. With this were compared gliadin and edestin as rep- 
resentatives of the vegetable proteins differing quite widely from those of the 
body and casein as an animal protein more or less similar to the tissue proteins. 

The series of experiments on the first dog affords a striking illustration of 
the difficulties in the way of successful investigation of this question. After 
fasting for 16 days and receiving only nonnitrogenous feed 1 (sugar and lard) 
for 28 days more, the daily nitrogen excretion (feces and urine) was reduced 
to 1.42 grams per day and appeared to have become approximately constant. 
Quantities of the various protein materials containing this amount of nitrogen 
were then added in successive periods to the basal nonnitrogenous ration and 
the effect upon the nitrogen balance determined, the periods covering from 6 
to 9 days each. In three periods in which dog flesh was fed, the animal 
gained small amounts of nitrogen (0.08 to 0.17 gram per day) ; in other words, 
an amount of protein equal to the fasting katabolism sufficed to produce nitro- 
gen equilibrium. Practically the same result was also attained in the period 
in which " Nutrose " (a preparation of casein) was fed. Three periods with 
gliadin, on the contrary, showed in every case a loss of nitrogen ranging from 
0.33 to 0.52 gram per day ; that is, the gliadin appeared decidedly less valuable 
than the dog flesh or casein for the maintenance of the body protein. Upon 
adding more gliadin to the ration it was found necessary to increase the daily 
amount to the equivalent of about 3.5 grams of nitrogen before nitrogen equilib- 
rium was reached. 

At the conclusion of this series, however, two 3-day periods on the nitrogen- 
free ration (preceding and following the period with the larger amount of 
gliadin) showed that the prolonged feeding on rations poor in protein had so 
lowered the plane of protein nutrition that the daily fasting katabolism was 
now equivalent to only 0.95 gram of nitrogen, or on the average of the last 
two days of each period to only 0.82 gram. In other words, the 1.42 grams of 
the earlier periods did not represent the absolute minimum on which life 
could be maintained. A second series of trials was therefore instituted in 
which dog tissue was compared with casein and edestin. In no case was 
nitrogen equilibrium quite reached, but the dog flesh still showed a decided 
advantage over the other forms of protein. The dog, however, had become 
very much reduced and died during the final period on dog flesh, the autopsy 
showing an exceedingly anemic condition. The attempt to base the compari- 
sons of the different proteins upon the absolute minimum of the protein 
katabolism, in other words, involved such a reduction in the stock of body 
protein and consequently such an abnormal condition of the animal as to render 
the value of the results questionable. In succeeding experiments on two other 
dogs, therefore, the attempt to reach the absolute minimum of the protein 
katabolism was abandoned and the amounts of the several proteins added to 
the basal nonnitrogenous ration were either made equivalent to the fasting 
katabolism in the first period or reduced slightly below it according to the 
judgment of the experimenter. The results were in accord with those of the 
first series, the vegetable proteins, gliadin and edestin. proving notably inferior 
to the dog flesh or the casein. 

1 No mention is made of any supply of ash ingredients other than those contained in 
the various forms of protein used, with the exception of a small amount of calcium car- 
bonate (p. 423). 



104 



MAINTENANCE RATIONS OF FARM ANIMALS. 



Upon two points, however, Michaud's results seem open to question. 

First, the pure proteins which he employed, as well as the sugar and lard, 
can have contained but minimal amounts of ash, while, as already stated, no 
mention is made of the addition of any ash ingredients except calcium car- 
bonate. In those periods, then, the animal was apparently in a state of par- 
rial or entire mineral hunger. The dog flesh (or in two periods horse flesh), 
on the other hand, contained its normal amount of ash, and it is not im- 
possible that this was an important factor in determining its higher value, 
although it must be admitted that this explanation does not apply to the 
casein periods. Second, dog tissue or horse flesh is by no means pure protein, 
but in addition to ash constituents contains a great variety of organic com- 
pounds, which may have been quite as important as the protein. In other 
words, the periods on tissue are not comparable with those on pure proteins. 

zisterer's experiments. 

Zisterer 1 has reported two series of similar experiments, also on a dog. 
They differed from Michaud's, however, in that the periods were shorter and 
that each feeding period was interpolated between two periods on a nonnitro- 
genous basal ration from the average results of which the fasting protein 
katabolism of the animal for that particular bodily condition was computed. 
Zisterer experimented with casein, wheat gluten, and lean meat extracted 
with water (muscle protein). He added to his rations the chlorids of sodium, 
potassium, and calcium, but no other ash ingredients. The ash content of 
the feeds was small. The energy supply in the feed was in every instance 
ample to supply the needs of the animal as computed according to E. Voit. 2 
Taking the first period, on casein, as an example, the preliminary period on 
nitrogen-free feed covered five days and the one following the feeding period 
four days. On the average of the last two days of these periods, the fasting 
protein katabolism was equivalent to 1.975 grams nitrogen daily. During the 
intermediate 4-day period, casein containing 2.018 grams nitrogen per day 
was fed and the average daily nitrogen excretion for the last two days was 
found to be 2.333 grams. Two series of trials of this sort, made in inverse 
order, yielded the following results: 



Protein metabolism of a dog — Zisterer. 





Fasting 
nitrogen 
katabolism. 


Feed 
nitrogen. 


Total 
nitrogen 
excretion. 


Gain of 
nitrogen 
by animal. 


Series I: 


Grams. 


Grams. 


Grams. 


Grams. 




1.975 


2. 018 


2. 333 


-0.315 




2.125 


2.021 


2.316 


- .294 


Wheat gluten 


1.951 


2.017 


2.113 


- .096 


Series II: 










Wheat gluten 


1.800 


2.111 


2.276 


- .1C5 


Muscle protein 


1.806 


2.110 


1.903 


+ .207 


Casein 


1.708 


2.108 


2.050 


+ .058 


Average: 










Casein 


1.842 


2.063 


2.192 


- .129 


Muscle protein 


1.966 


2. 066 


2.109 


+ .043 


Wheat gluten 


1.876 


2.064 


2. 195 


+ .131 



If we represent the total nitrogen excretion upon the muscle protein by 100, 
That observed with the other proteins was as follows: 



1 Zoitschrift fur Biologie, vol. 53, p. 157. 



- Ibid., vol. 41, p. 113. 



RELATIVE VALUES OF PROTEINS. 105 



Relative nitrogen excretion on different proteins. 





Series I. 


Series II. 


Average. 




101 
100 
91 


108 
100 
120 


104 
100 
104 




Wheat gluten 





Compared in this way, the differences disclosed between the different pro- 
teins are small in themselves, and, especially in the case of the wheat gluten, 
are discordant in the two series. Apparently the differences are less than those 
which may be plausibly ascribed to variations in the conditions of the several 
experiments. The latter may be to some degree eliminated by comparing the 
total nitrogen excretion with the fasting nitrogen katabolism of the corre- 
sponding periods. If the latter be represented by 100, the relative nitrogen 
excretion on the several proteins was as follows : 





Series I. 


Series II. 


Average. 


Casein 


118.1 
109.0 
108.3 


120.0 
105.4 
126.5 


119.1 
107.2 
117.4 


Muscle protein 


Wheat gluten 





This second method of comparison seems to indicate a distinct, although 
small, inferiority of the casein as compared with the muscle protein. The 
same is true of the average result with wheat gluten, but not of the results 
of the individual series. Entirely similar results are obtained if the calcula- 
tion is made only upon the protein nitrogen of the feed and excreta instead of 
the total nitrogen. Zisterer's results are, of course, open to the same criticism 
made on Michaud's, viz, that the so-called muscle protein was not comparable 
with the pure proteins used in the other periods. 

RESULTS ABE QUALITATIVE. 

Both Michaud's and Zisterer's results are in a sense qualitative. They show 
that certain foreign proteins when substituted for tissue caused a relatively 
greater nitrogen excretion and were therefore less efficient in maintaining the 
nitrogen balance of the body. For gliadin and edestin, Michaud observed a nota- 
bly greater difference than did Zisterer for wheat gluten. For casein their results 
are quite similar. In no case was the amount of foreign protein required to 
reach nitrogen equilibrium determined, with the exception of one short period 
upon gliadin in Michaud's experiments. In both cases, the differences appear 
relatively small. On the basis of average figures for the proportions of four of 
the principal amino-acids in the different proteins, Zisterer computes much 
greater possible differences. Representing the amount of muscle protein re- 
quired to furnish a given amount of each one of the four amino-acids by 100, 
Zisterer calculates that .the following amounts of casein and of wheat gluten 
would be required for the same purpose : 





Muscle 
protein. 


Casein. 


Wheat 
gluten. 


To furnish equal amounts of : 

Alanin 


100 
100 
100 
100 


444 
74 

124 
47 


267 
154 
49 
102 


Leucin 


Glutamic acid 


Tyrosin , 





106 



MAINTENANCE RATIONS OF FARM ANIMALS. 



As was noted above, the ash supply was but partially considered in Zisterer's 
experiments, no mention being made of the addition of ash ingredients with the 
exception of sodium, potassium, and calcium. It seems not impossible that the 
phosphorus compounds of the muscle protein may have had something to do 
with its apparently greater availability. 



THOMAS'S EXPERIMENTS. 



Thomas 1 has attempted to determine the relative values of the mixed proteins 
of different foods by a method differing somewhat from that employed in the 
two foregoing investigations. As has been shown in previous pages, on an 
abundant nonnitrogenous ration, especially of carbohydrates, the protein 
katabolism of the body may be reduced to a very low limit which represents 
more or less exactly the minimum amount of protein necessarily broken down 
in the vital activities. If a small amount of protein be added to such a non- 
nitrogenous ration, it will tend to be used to replace body protein, since the 
surplus of nonnitrogenous material tends to prevent its being katabolized to 
furnish energy. The extent, then, to which any given protein under these con- 
ditions diminishes the loss of protein from the body may be taken as the 
measure of its maintenance value. The principle of the method may be illus- 
trated by the following supposititious case. 



Protein digested 

Protein katabolized 

Loss of protein from body. 



On protein- 
free food. 



On protein 
food. 



In this case, four parts of food protein obviously replace three parts of body 
protein and the percentage availability of the former is therefore 75. The 
principle of the method is similar to that of the determination of the percentage 
availability of energy (p. 27). 

It is to be remarked concerning this method, first, that it assumes that the 
percentage availability of the food protein is the same for all amounts below 
the maintenance requirement; in other words, that it is a linear function. 
This is an unproved assumption, and in view of the readiness with which 
protein or its cleavage products in the body seem to be deamidized and utilized 
as fuel, the assumption seems of questionable validity. 

Second, in applying the method it is necessary to know accurately the mini- 
mum amount of protein katabolized on a nitrogen-free diet, since any error in 
the determination of its quantity seriously affects the final result. The protein 
katabolism, however, under these conditions, is not a constant quantity, as 
has already been pointed out, but varies more or less, especially with the state 
of protein nutrition of the cells. Accordingly, it must be determined as accu- 
rately as possible for the subject at the time of the experiment, preferably 
immediately before and immediately after. 

Third, the amount of protein fed must be less than that katabolized on the 
nitrogen-free diet. If an excess of protein be consumed, the additional amount 
will tend to be katabolized and used as fuel, thus rendering the comparison 
between the two periods illusory, since it is obvious that any such oxidation 
of protein would tend to make its availability appear too low. Thomas's 
experiments were made upon himself and included four series, two in May to 



iArchiv fiir (Anatomie und) Physiologie, 1909, p. 219. 



RELATIVE VALUES OF PEOTEINS. 



107 



July and two in September to November of the same year. He determined, bis 
protein katabolism upon a nonnitrogenous diet (chiefly carbohydrates) in three 
or four day periods in each series and also interpolated single nitrogen-free 
days during each series. The results of these periods were more or less vari- 
able, but the final values employed by him, although representing to some de- 
gree an arbitrary selection of days, seem, on the whole, to fairly represent the 
nitrogen katabolism ; that is, they satisfy the second of the two conditions 
above pointed out. 

With these values for the protein katabolism were compared the nitrogen 
balances of periods of from two to four days (or in a few cases only one day) 
in which single foods were consumed along with sufficient carbohydrates and 
fat to fully supply the demands of the body for energy. The technic of these 
periods, however, can hardly be regarded as entirely satisfactory. Out of 33 
days, the results of which are contained in his final table, the protein digested 
was greater than the average protein katabolism on the nitrogen-free days in 
21 cases, the difference sometimes being considerable and sometimes relatively 
insignificant. As already pointed out, this tended to make the availability 
appear too low, and it is noteworthy that the excess of food protein is especially 
large in the experiments upon wheat flour which show a strikingly low avail- 
ability. On the other hand, however, it is also true that a very low availability 
was found for maize protein in experiments in which but a slight excess was 
fed. In these experiments, however, the apparent digestibility of the protein 
was remarkably low, ranging from 56 to 69 per cent, but a similar low digesti- 
bility (about 68 per cent) was found in the trials with rice. Furthermore, the 
periods were relatively short and in many instances the nitrogen intake varied 
considerably within the period, so that it may be questioned whether the nitro- 
gen excretion reached a stable value. Moreover, to some extent there was a 
more or less arbitrary selection of days to be compared. For all these reasons 
Thomas's results must be accepted with more or less reserve. 

His final results for the percentage availability of the protein of different 
materials are as follows, the results being calculated in three different 
ways, viz : 

A. Fecal nitrogen all regarded as derived from the food, that is, the compari- 
son is made upon the basis of the apparently digested protein. 

B. Fecal nitrogen regarded as being all present in the form of metabolic 
products. 

C. One gram of fecal nitrogen is regarded as derived from metabolic products 
and the remainder from undigested food. 



Relative availability of proteins — Thomas. 





1 

A. B. 

! 


C. 


Lean beef 


/ 104.94 
\ 106.51 

99. 65 
f 103. 09 
\ 85. 73 
{ 88. 17 
/ 83.00 
\ 86. 26 
( 72. 60 
\ 73. 38 
/ 56.63 
\ 53. 40 

66.69 

63.45 
{ 29. 17 

36. 70 
\ 64. 50 

41. 35 
{ 27. 74 


103. 75 
L05. 73 
99. 71 
L02. 06 
89.37 
91.95 
88. 53 
90. 73 
78. 85 
79.45 
73.48 
70. 35 
70. 14 
69. 02 
36. 25 
43.04 
42.04 
51.10 
39. 75 




Milk 




Fish 




Rice 


87.09 
89.55 


Crabs 


Yeast 


69. 58 
71.45 
67. 12 


Casein 


Nutrose 








48. 97 

36. 94 



108 MAINTENANCE RATIONS OF FARM ANIMALS. 



Relative availability of proteins — Thomas — Continued. 





A. 


B. 


C. 


Potatoes 


f 56.37 
64. 50 
73. 00 
80. 33 
77. 04 
78. 66 
1 80. 68 
\ 77. 62 
64. 50 
j 49. 58 
\ 51.64 
66.42 
f 24.55 
< 12. 25 




68.80 
72.67 
78.72 







Cauliflower 


83. 18 


76.22 
77.45 
87. 78 
83.88 
63.83 
55.15 
56.01 
78.57 
40.47 
29. 52 
3.54 












59. 89 
59. 89 




Maize I 















In Zisterer's experiments, summarized on page 104, the feed nitrogen is 
so slightly in excess of the fasting nitrogen katabolism that it would seem that 
no large error would result from applying Thomas's method of computation. 
The results are as follows : 



Percentage availability. 





Series I. 


Series II. 


Average. 


Casein 


82. 26 
90. 60 
91.97 


83. 77 
95.40 
77.45 


83.02 
93.00 
84. 71 


Muscle protein 


Wheat gluten 





The results as thus computed are not widely different from those obtained 
by Thomas for casein and meat protein, but are slightly higher than his results 
for wheat protein. Michaud's results do not lend themselves to computation in 
this way. 

Another recent investigation of a different character may be mentioned for 
the sake of completeness, viz, that on frogs by Busquet, 1 who compared lean 
veal and mutton with frog meat as regards the amount required to maintain 
the live weight or to produce a unit of gain of weight in previously fasting 
frogs. In this respect the veal and mutton were found distinctly inferior to the 
frog meat per unit of dry matter. 

SIGNIFICANCE OF RESULTS. 

In the comments upon the individual experiments, it has already 
been clearly indicated that they are open to criticism in many re- 
spects, such as the noncomparable nature of the protein supply, the 
lack of due consideration of the supply of mineral matter, etc. 
Moreover, nearly all the experiments were of relatively short 
duration. 

Taking the results at their face value, however, they seem to in- 
dicate distinct differences in the nutritive values of proteins. The 
entire lack of certain groups, as in the case of gelatin and zein, 



1 Journal de Physiologic et de Pathologie Generale, vol. 11, p. 399. 



RELATIVE, VALUES OF PROTEINS. 



109 



seems to render impossible a complete substitution for tissue pro- 
tein, while differences in the proportions of the different amino 
acids apparently result in differences in the replacement values of 
the proteins, although these differences, especially in the experiments 
of Michaud and Zisterer, are hardly as great as might have been 
expected. What now can be said regarding the probable significance 
of these differences for the ordinary problems of nutrition ? 

In the first place, it is to be remarked that both man and animals 
consume a mixture of proteins. The meat eater gets, along with 
his gelatin, the various muscle proteins. The animal fed on maize 
alone receives not only zein but its associated proteins, amounting, 
according to Osborne, 1 to about 40 per cent of the total protein of 
the grain, whose chemical constitution has not yet been reported. 
In the ordinary mixed rations of domestic animals it would appear 
that there must be a considerable degree of compensation between 
the different proteins as regards the proportions of the different 
cleavage products supplied to the organism, although it is difficult 
to judge to what extent this is the case. In view, however, of the 
rather small differences observed with pure proteins, it may be 
questioned whether such differences as exist in mixed rations are of 
very much significance. 

In the second place, the observed differences in proteins were ob- 
tained in experiments in which small amounts of protein were con- 
sumed and in which the animals were on a low level of protein 
nutrition. As was pointed out in the discussion of those experiments, 
the consumption of protein in excess of the maintenance requirement, 
such as usually occurs with domestic animals, tends to obscure the 
differences between the proteins, owing to the considerable extent to 
which protein serves for fuel purposes under those conditions. 

Third, almost all writers upon this subject tacitly assume the in- 
ability of the body to change one amino- acid into another. It does 
not appear that there is adequate proof of this inability. Most of 
the amino acids concerned belong to the aliphatic series of com- 
pounds, characterized by a straight carbon chain, and as between 
these compounds, at least, mutual changes are not difficult to conceive. 
As a matter of fact one such change appears to have been dem- 
onstrated. It is well known that when benzoic acid is consumed it 
is paired in the body with glycocol, forming hippuric acid which is 
excreted. It seems to be well established that with large amounts of 
benzoic acid more combined glycocol may appear in the excreta than 
can be assumed to have been present as such in the amount of protein 
katabolized during the same time. In this case, apparently, the body 
is able to manufacture glycocol from some other substance, pre- 

1 Journal of the American Chemical Society, vol. 19, p. 532. 



110 



MAINTENANCE RATIONS OF FARM ANIMALS. 



snmably from the amino-acids containing a larger number of carbon 
atoms. Whether a change in the opposite direction, that is, a syn- 
thetic change, can take place can be at present only a matter of specu- 
lation, but such a change would be entirely analogous to the building 
up of the fatty-acid chains from carbohydrates, which is a common 
occurrence in the body. Moreover, Knoop, 1 and Embden and 
Schmitz 2 have found that certain amino acids may be formed syn- 
thetically from the corresponding fatty acids and ammonia, thus 
indicating a possible chemical mechanism by which a deficient sup- 
ply of some one amino-acid might be to some extent overcome. While, 
therefore, we can hardly suppose that the proportions of the different 
cleavage products is a matter of entire indifference, we can easily 
imagine that there may be more or less transformation of one into 
another in case of need. 

Finally, there is the possibility that in the absence of some one 
amino-acid from the feed, the corresponding acid resulting from the 
katabolism of protein tissue may to a greater or less extent escape the 
action of the deamidizing enzyms and be regenerated to protein. 
This would obviously be quite in accord with the conception of the 
protein metabolism as a complex of reversible enzym reactions which 
was outlined on page 87. 

1 Zeitschrif t fur Physiologische Chemie, vol. 67, p. 489. 

2 Biochemische Zeitschrift, vol. 29, p. 423. 



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